diff --git a/src/univers/datetime.py b/src/univers/datetime.py
index 264c164d..cee2c270 100644
--- a/src/univers/datetime.py
+++ b/src/univers/datetime.py
@@ -105,6 +105,9 @@ def __gt__(self, other):
     def __ge__(self, other):
         return self.parsed_stamp >= other.parsed_stamp
 
+    def __str__(self):
+        return self.original
+
     @classmethod
     def is_valid(cls, string):
         return bool(cls.VERSION_PATTERN.fullmatch(string))
diff --git a/src/univers/intdot.py b/src/univers/intdot.py
index b48af4d5..ebd805af 100644
--- a/src/univers/intdot.py
+++ b/src/univers/intdot.py
@@ -36,6 +36,9 @@ def __gt__(self, other):
     def __ge__(self, other):
         return self.__cmp__(other) >= 0
 
+    def __str__(self):
+        return self.original
+
     @classmethod
     def is_valid(cls, string):
         return re.compile(IntdotVersion.VERSION_PATTERN).match(string)
diff --git a/src/univers/utils.py b/src/univers/utils.py
index 63952ce4..d8cb07d4 100644
--- a/src/univers/utils.py
+++ b/src/univers/utils.py
@@ -9,6 +9,13 @@ def remove_spaces(string):
     return "".join(string.split())
 
 
+ASCII_WHITESPACE = frozenset(" \t\n\r\f\v")
+
+
+def contains_ascii_whitespace(string):
+    return any(character in ASCII_WHITESPACE for character in string)
+
+
 def cmp(x, y):
     """
     Replacement for built-in Python 2 function cmp that was removed in Python 3
diff --git a/src/univers/version_constraint.py b/src/univers/version_constraint.py
index 2613a487..b30265f0 100644
--- a/src/univers/version_constraint.py
+++ b/src/univers/version_constraint.py
@@ -9,6 +9,7 @@
 
 import attr
 
+from univers.utils import contains_ascii_whitespace
 from univers.utils import remove_spaces
 from univers.versions import Version
 
@@ -166,7 +167,10 @@ def from_string(cls, string, version_class):
         Return a single VersionConstraint built from a constraint ``string`` and
         a ``version_class`` Version class.
         """
-        constraint_string = remove_spaces(string)
+        if contains_ascii_whitespace(string):
+            raise ValueError(f"Invalid ASCII whitespace in constraint: {string!r}")
+
+        constraint_string = string
 
         # A version range specifier contains only printable ASCII letters, digits and
         # punctuation.
@@ -195,7 +199,7 @@ def split(string):
 
         For example::
         >>> assert VersionConstraint.split(">=2.3") == (">=", "2.3",)
-        >>> assert VersionConstraint.split("  <   =  2 . 3  ") == ("<=", "2.3",)
+        >>> assert VersionConstraint.split("<=2.3") == ("<=", "2.3",)
         >>> assert VersionConstraint.split("2.3") == ("=", "2.3",)
         >>> assert VersionConstraint.split("*2.3") == ("*", "",)
         >>> assert VersionConstraint.split("*") == ("*", "",)
@@ -208,7 +212,10 @@ def split(string):
         ... except ValueError:
         ...     pass
         """
-        constraint_string = remove_spaces(string)
+        if contains_ascii_whitespace(string):
+            raise ValueError(f"Invalid ASCII whitespace in constraint: {string!r}")
+
+        constraint_string = string
 
         # special case for star
         if constraint_string.startswith("*"):
@@ -292,13 +299,13 @@ def validate(cls, constraints):
         # occur only once in any ``<version-constraint>`` of a range specifier,
         # irrespective of its comparators. Tools must report an error for duplicated
         # versions.
-        if len(set(c.version for c in constraints)) != len(constraints):
-            raise ValueError(f"{constraints!r} cannot contain duplicated Version")
+        for index, constraint in enumerate(constraints):
+            if any(constraint.version == other.version for other in constraints[index + 1 :]):
+                raise ValueError(f"{constraints!r} cannot contain duplicated Version")
 
-        # Constraints are sorted by version**. The canonical ordering is the versions
-        # order. The ordering of ``<version-constraint>`` is not significant otherwise
-        # but this sort order is needed when check if a version is contained in a range.
-        constraints.sort()
+        sorted_constraints = sorted(constraints)
+        if list(constraints) != sorted_constraints:
+            raise ValueError(f"{constraints!r} must use canonical ordering by version")
 
         return validate_comparators(constraints)
 
diff --git a/src/univers/version_range.py b/src/univers/version_range.py
index c50bc87c..97c237a6 100644
--- a/src/univers/version_range.py
+++ b/src/univers/version_range.py
@@ -18,6 +18,7 @@
 from univers import maven
 from univers import versions
 from univers.conan.version_range import VersionRange as conan_version_range
+from univers.utils import contains_ascii_whitespace
 from univers.utils import remove_spaces
 from univers.version_constraint import VersionConstraint
 from univers.version_constraint import contains_version
@@ -108,8 +109,10 @@ def from_string(cls, vers, simplify=False, validate=False):
                 f"{vers!r} is not a valid argument, a valid ``vers`` string argument is required."
             )
 
-        # Spaces are not significant and removed in a canonical form.
-        vers = remove_spaces(vers)
+        if contains_ascii_whitespace(vers):
+            raise ValueError(f"Invalid ASCII whitespace in VERS string: {vers!r}")
+
+        original_vers = vers
 
         # A version range specifier contains only printable ASCII letters, digits and
         # punctuation.
@@ -134,7 +137,6 @@ def from_string(cls, vers, simplify=False, validate=False):
 
         version_class = range_class.version_class
 
-        constraints = remove_spaces(constraints)
         if not constraints:
             raise ValueError(f"{vers!r} specifies no version range constraints.")
 
@@ -149,7 +151,12 @@ def from_string(cls, vers, simplify=False, validate=False):
 
         parsed_constraints = []
 
-        constraints = constraints.strip("|")
+        if constraints.startswith("|") or constraints.endswith("|"):
+            raise ValueError(f"{vers!r} contains a leading or trailing pipe '|'.")
+
+        if "||" in constraints:
+            raise ValueError(f"{vers!r} contains consecutive pipes '||'.")
+
         for const in constraints.split("|"):
             constraint = VersionConstraint.from_string(
                 string=const,
@@ -157,17 +164,19 @@ def from_string(cls, vers, simplify=False, validate=False):
             )
             parsed_constraints.append(constraint)
 
-        # Constraints are sorted by version**. The canonical ordering is the versions
-        # order. The ordering of ``<version-constraint>`` is not significant otherwise
-        # but this sort order is needed when check if a version is contained in a range.
-        parsed_constraints.sort()
+        VersionConstraint.validate(parsed_constraints)
 
         if simplify:
             parsed_constraints = VersionConstraint.simplify(parsed_constraints)
         if validate:
             VersionConstraint.validate(parsed_constraints)
 
-        return range_class(parsed_constraints)
+        version_range = range_class(parsed_constraints)
+        canonical_vers = str(version_range)
+        if canonical_vers != original_vers:
+            raise ValueError(f"{original_vers!r} is not canonical. Expected {canonical_vers!r}.")
+
+        return version_range
 
     @classmethod
     def from_versions(cls, sequence):
diff --git a/tests/data/schema/range/pypi_range_containment.json b/tests/data/schema/range/pypi_range_containment.json
index d4b232bf..3998f5c8 100644
--- a/tests/data/schema/range/pypi_range_containment.json
+++ b/tests/data/schema/range/pypi_range_containment.json
@@ -44,7 +44,7 @@
     "test_group": "advanced",
     "test_type": "containment",
     "input": {
-      "vers": "vers:pypi/>=3.0.0|2.0.3",
+      "vers": "vers:pypi/2.0.3|>=3.0.0",
       "version": "2.0.3"
     },
     "expected_output": true
@@ -74,7 +74,7 @@
     "test_group": "advanced",
     "test_type": "containment",
     "input": {
-      "vers": "vers:pypi/>=3.0.0|!=2.0.3",
+      "vers": "vers:pypi/!=2.0.3|>=3.0.0",
       "version": "2.0.3"
     },
     "expected_output": false
@@ -94,7 +94,7 @@
     "test_group": "advanced",
     "test_type": "containment",
     "input": {
-      "vers": "vers:pypi/0.0.2|0.0.6|>=3.0.0|0.0.1|0.0.4|0.0.5|0.0.3",
+      "vers": "vers:pypi/0.0.1|0.0.2|0.0.3|0.0.4|0.0.5|0.0.6|>=3.0.0",
       "version": "2.0.3"
     },
     "expected_output": false
diff --git a/tests/data/schema/range/pypi_range_roundtrip.json b/tests/data/schema/range/pypi_range_roundtrip.json
index da9a6dd2..583a08a5 100644
--- a/tests/data/schema/range/pypi_range_roundtrip.json
+++ b/tests/data/schema/range/pypi_range_roundtrip.json
@@ -13,7 +13,7 @@
     "test_group": "advanced",
     "test_type": "roundtrip",
     "input": {
-      "vers": "vers:pypi/0.0.2|0.0.6|0.0.0|0.0.1|0.0.4|0.0.5|0.0.3"
+      "vers": "vers:pypi/0.0.0|0.0.1|0.0.2|0.0.3|0.0.4|0.0.5|0.0.6"
     },
     "expected_output": "vers:pypi/0.0.0|0.0.1|0.0.2|0.0.3|0.0.4|0.0.5|0.0.6"
   },
@@ -22,27 +22,27 @@
     "test_group": "advanced",
     "test_type": "roundtrip",
     "input": {
-      "vers": "vers:pypi/>0.0.0|>=0.0.1|0.0.2|<0.0.3|0.0.4|<0.0.5|>=0.0.6"
+      "vers": "vers:pypi/0.0.2|0.0.4|>=0.0.6"
     },
-    "expected_output": "vers:pypi/>0.0.0|>=0.0.1|0.0.2|<0.0.3|0.0.4|<0.0.5|>=0.0.6"
+    "expected_output": "vers:pypi/0.0.2|0.0.4|>=0.0.6"
   },
   {
     "description": "Roundtrip test for pypi VERS range.",
     "test_group": "advanced",
     "test_type": "roundtrip",
     "input": {
-      "vers": "vers:pypi/>0.0.0|>=0.0.1|>=0.0.1|0.0.2|0.0.3|0.0.4|<0.0.5|<=0.0.6|!=0.7|8.0|>12|<15.3"
+      "vers": "vers:pypi/!=0.7|8.0|>12|<15.3"
     },
-    "expected_output": "vers:pypi/>0.0.0|>=0.0.1|>=0.0.1|0.0.2|0.0.3|0.0.4|<0.0.5|<=0.0.6|!=0.7|8.0|>12|<15.3"
+    "expected_output": "vers:pypi/!=0.7|8.0|>12|<15.3"
   },
   {
     "description": "Roundtrip test for pypi VERS range.",
     "test_group": "advanced",
     "test_type": "roundtrip",
     "input": {
-      "vers": "vers:pypi/>0.0.0|>=0.0.1|0.0.2|0.0.3|0.0.4|<0.0.5|>=0.0.6|!=0.8"
+      "vers": "vers:pypi/>0.0.0|<0.0.5|>=0.0.6|!=0.8"
     },
-    "expected_output": "vers:pypi/>0.0.0|>=0.0.1|0.0.2|0.0.3|0.0.4|<0.0.5|>=0.0.6|!=0.8"
+    "expected_output": "vers:pypi/>0.0.0|<0.0.5|>=0.0.6|!=0.8"
   },
   {
     "description": "Roundtrip test for pypi VERS range.",
@@ -166,7 +166,7 @@
     "test_group": "advanced",
     "test_type": "roundtrip",
     "input": {
-      "vers": "vers:pypi/0.0.2|0.0.6|>=0.0.0|0.0.1|0.0.4|0.0.5|0.0.3"
+      "vers": "vers:pypi/>=0.0.0|0.0.1|0.0.2|0.0.3|0.0.4|0.0.5|0.0.6"
     },
     "expected_output": "vers:pypi/>=0.0.0|0.0.1|0.0.2|0.0.3|0.0.4|0.0.5|0.0.6"
   }
diff --git a/tests/data/schema/range/vers_parse_canonical.json b/tests/data/schema/range/vers_parse_canonical.json
new file mode 100644
index 00000000..124ba971
--- /dev/null
+++ b/tests/data/schema/range/vers_parse_canonical.json
@@ -0,0 +1,64 @@
+{
+  "$schema": "https://packageurl.org/schemas/vers-test.schema-0.1.json",
+  "tests": [
+    {
+      "description": "Canonical parse succeeds for an already normalized VERS.",
+      "test_group": "base",
+      "test_type": "parse",
+      "input": "vers:npm/>=1.0.0|<2.0.0",
+      "expected_output": {
+        "scheme": "npm",
+        "version_constraints": [
+          [
+            ">=",
+            "1.0.0"
+          ],
+          [
+            "<",
+            "2.0.0"
+          ]
+        ]
+      }
+    },
+    {
+      "description": "Parsing fails when ASCII whitespace is present.",
+      "test_group": "base",
+      "test_type": "parse",
+      "input": "vers:npm/>=1.0.0| <2.0.0",
+      "expected_failure": true,
+      "expected_failure_reason": "non-canonical VERS: whitespace is not permitted"
+    },
+    {
+      "description": "Parsing fails when constraints start with a pipe.",
+      "test_group": "base",
+      "test_type": "parse",
+      "input": "vers:npm/|>=1.0.0|<2.0.0",
+      "expected_failure": true,
+      "expected_failure_reason": "non-canonical VERS: leading pipe is not permitted"
+    },
+    {
+      "description": "Parsing fails when constraints end with a pipe.",
+      "test_group": "base",
+      "test_type": "parse",
+      "input": "vers:npm/>=1.0.0|<2.0.0|",
+      "expected_failure": true,
+      "expected_failure_reason": "non-canonical VERS: trailing pipe is not permitted"
+    },
+    {
+      "description": "Parsing fails when constraints contain consecutive pipes.",
+      "test_group": "base",
+      "test_type": "parse",
+      "input": "vers:npm/>=1.0.0||<2.0.0",
+      "expected_failure": true,
+      "expected_failure_reason": "non-canonical VERS: consecutive pipes are not permitted"
+    },
+    {
+      "description": "Parsing fails when constraints are not in canonical order.",
+      "test_group": "base",
+      "test_type": "parse",
+      "input": "vers:npm/>=2.0.0|<1.0.0",
+      "expected_failure": true,
+      "expected_failure_reason": "non-canonical VERS: constraints are not sorted by version"
+    }
+  ]
+}
\ No newline at end of file
diff --git a/tests/test_version_constraint.py b/tests/test_version_constraint.py
index 9997b7c7..a5638295 100644
--- a/tests/test_version_constraint.py
+++ b/tests/test_version_constraint.py
@@ -96,3 +96,12 @@ def test_invalid_vers_comparator_prefixes(spec):
             string=spec,
             version_class=versions.SemverVersion,
         )
+
+
+@pytest.mark.parametrize("spec", [">= 2.3", "\t>=2.3", ">=2.3\n"])
+def test_invalid_vers_constraint_with_ascii_whitespace(spec):
+    with pytest.raises(ValueError, match="ASCII whitespace"):
+        VersionConstraint.from_string(
+            string=spec,
+            version_class=versions.SemverVersion,
+        )
diff --git a/tests/test_version_range.py b/tests/test_version_range.py
index b2cb3c4a..927c2020 100644
--- a/tests/test_version_range.py
+++ b/tests/test_version_range.py
@@ -59,6 +59,52 @@
 TEST_DATA_PYPI_CONTAINMENT = TEST_DATA_PARENT / "pypi_range_containment.json"
 
 TEST_DATA_PYPI_ROUNDTRIP = TEST_DATA_PARENT / "pypi_range_roundtrip.json"
+TEST_DATA_VERS_PARSE_CANONICAL = TEST_DATA_PARENT / "vers_parse_canonical.json"
+
+
+def assert_parse_failure_reason(error_message, expected_reason):
+    message = error_message.lower()
+    reason = expected_reason.lower()
+
+    if "whitespace" in reason:
+        assert "whitespace" in message
+        return
+
+    if "leading pipe" in reason or "trailing pipe" in reason:
+        assert "leading or trailing pipe" in message
+        return
+
+    if "consecutive pipes" in reason:
+        assert "consecutive pipes" in message
+        return
+
+    if "sorted by version" in reason:
+        assert "canonical ordering" in message
+        return
+
+    assert reason in message
+
+
+@pytest.mark.parametrize("test_case", json.load(open(TEST_DATA_VERS_PARSE_CANONICAL))["tests"])
+def test_vers_spec_parse_cases(test_case):
+    vers_string = test_case["input"]
+
+    if test_case.get("expected_failure"):
+        with pytest.raises(ValueError) as error:
+            VersionRange.from_string(vers_string)
+
+        expected_failure_reason = test_case.get("expected_failure_reason")
+        if expected_failure_reason:
+            assert_parse_failure_reason(str(error.value), expected_failure_reason)
+        return
+
+    version_range = VersionRange.from_string(vers_string)
+    expected_output = test_case["expected_output"]
+
+    assert version_range.scheme == expected_output["scheme"]
+    assert [
+        [constraint.comparator, str(constraint.version)] for constraint in version_range.constraints
+    ] == expected_output["version_constraints"]
 
 
 class TestVersionRangeContainment(SchemaDrivenVersTest):
@@ -244,6 +290,23 @@ def test_alpine_version_range_containment():
     assert AlpineLinuxVersion("3.19.0") not in vr
 
 
+@pytest.mark.parametrize(
+    "vers, expected_error",
+    [
+        ("vers:pypi/>= 1.0", "ASCII whitespace"),
+        ("vers:pypi/|>=1.0", "leading or trailing pipe"),
+        ("vers:pypi/>=1.0|", "leading or trailing pipe"),
+        ("vers:pypi/>=1.0||<2.0", "consecutive pipes"),
+        ("vers:pypi/>=2.0|>=1.0", "canonical ordering"),
+        ("vers:pypi/>=1.0|<=1.0", "duplicated Version"),
+        ("vers:pypi/>=1.0|>2.0", "cannot be followed by"),
+    ],
+)
+def test_version_range_from_string_rejects_non_canonical_vers(vers, expected_error):
+    with pytest.raises(ValueError, match=expected_error):
+        VersionRange.from_string(vers)
+
+
 VERSION_RANGE_TESTS_BY_SCHEME = {
     "nginx": ["0.8.40+", "0.7.52-0.8.39", "0.9.10", "1.5.0+, 1.4.1+"],
     "npm": [
@@ -320,13 +383,13 @@ def test_mattermost_version_range():
         constraints=[
             VersionConstraint(comparator="=", version=SemverVersion("5.0")),
         ]
-    ) == VersionRange.from_string("vers:mattermost/5.0")
+    ) == VersionRange.from_string("vers:mattermost/5.0.0")
 
     assert MattermostVersionRange(
         constraints=[
             VersionConstraint(comparator=">=", version=SemverVersion("5.0")),
         ]
-    ) == VersionRange.from_string("vers:mattermost/>=5.0")
+    ) == VersionRange.from_string("vers:mattermost/>=5.0.0")
 
 
 def test_build_range_from_snyk_advisory_string():
@@ -453,8 +516,8 @@ def test_version_range_datetime():
 
 def test_version_range_lexicographic():
     assert LexicographicVersion("1.2.3") in VersionRange.from_string(
-        "vers:lexicographic/<1.2.4|>0.9"
+        "vers:lexicographic/>0.9|<1.2.4"
     )
     assert LexicographicVersion(-123) in VersionRange.from_string("vers:lexicographic/<~")
     assert LexicographicVersion(None) in VersionRange.from_string("vers:lexicographic/*")
-    assert LexicographicVersion("ABC") in VersionRange.from_string("vers:lexicographic/>abc|<=None")
+    assert LexicographicVersion("ABC") in VersionRange.from_string("vers:lexicographic/<=None|>abc")