diff --git a/test/test_advancedcpp.py b/test/test_advancedcpp.py
index 9d754e7..bf896c8 100644
--- a/test/test_advancedcpp.py
+++ b/test/test_advancedcpp.py
@@ -819,7 +819,6 @@ def test24_typedef_to_private_class(self):
 
         assert cppjit.gbl.TypedefToPrivateClass().f().m_val == 42
 
-    @mark.xfail(run=False, reason="Crashes")
     def test25_ostream_printing(self):
         """Mapping of __str__ through operator<<(ostream&)"""
 
diff --git a/test/test_boost.py b/test/test_boost.py
index bba20a1..157c066 100644
--- a/test/test_boost.py
+++ b/test/test_boost.py
@@ -1,7 +1,7 @@
 import os
 
 from pytest import mark, raises, skip
-from support import IS_MAC_ARM, IS_MAC_X86
+from support import IS_MAC_ARM, IS_MAC_X86, IS_VALGRIND
 
 # /usr/include and /usr/local/include are on the compiler's default search
 # path; the Homebrew (arm64) and MacPorts prefixes are not, so a hit there
@@ -35,7 +35,10 @@ def setup_class(cls):
         import cppjit
 
         add_boost_include_path()
-        cppjit.include("boost/any.hpp")
+        try:
+            cppjit.include("boost/any.hpp")
+        except ImportError:
+            skip("boost headers not loadable")
 
     @mark.skipif((IS_MAC_ARM or IS_MAC_X86), reason="Fails to include boost on OS X")
     def test01_any_class(self):
@@ -50,7 +53,11 @@ def test01_any_class(self):
 
         assert std.list[any]
 
-    @mark.xfail(run=False, reason="boost::any casting crashes")
+    @mark.xfail(
+        condition=IS_VALGRIND,
+        run=False,
+        reason="invalid reads in the JITed boost constructors under valgrind",
+    )
     def test02_any_usage(self):
         """boost::any assignment and casting"""
 
@@ -122,10 +129,17 @@ def setup_class(cls):
         import cppjit
 
         add_boost_include_path()
-        cppjit.include("boost/variant/variant.hpp")
-        cppjit.include("boost/variant/get.hpp")
+        try:
+            cppjit.include("boost/variant/variant.hpp")
+            cppjit.include("boost/variant/get.hpp")
+        except ImportError:
+            skip("boost headers not loadable")
 
-    @mark.xfail(run=False, reason="boost::variant access crashes")
+    @mark.xfail(
+        condition=IS_VALGRIND,
+        run=False,
+        reason="invalid reads in the JITed boost constructors under valgrind",
+    )
     def test01_variant_usage(self):
         """boost::variant usage"""
 
diff --git a/test/test_concurrent.py b/test/test_concurrent.py
index 6adea08..026fdcc 100644
--- a/test/test_concurrent.py
+++ b/test/test_concurrent.py
@@ -15,7 +15,6 @@ def setup_class(cls):
 
         cppjit.gbl.Workers.calc.__release_gil__ = True
 
-    @mark.xfail(run=False, reason="Crashes")
     def test01_simple_threads(self):
         """Run basic Python threads"""
 
@@ -35,7 +34,6 @@ def test01_simple_threads(self):
         for t in threads:
             t.join()
 
-    @mark.xfail(run=False, reason="Crashes")
     def test02_futures(self):
         """Run with Python futures"""
 
@@ -266,7 +264,6 @@ def test():
         for t in threads:
             t.join()
 
-    @mark.xfail(run=False, reason="Crashes")
     def test07_overload_reuse_in_threads_wo_gil(self):
         """Threads reuse overload objects; check for clashes if no GIL"""
 
diff --git a/test/test_lowlevel.py b/test/test_lowlevel.py
index b6ad122..0d8408e 100644
--- a/test/test_lowlevel.py
+++ b/test/test_lowlevel.py
@@ -669,7 +669,7 @@ def test15_templated_arrays_gmpxx(self):
         try:
             cppjit.include("gmpxx.h")
             cppjit.load_library("gmpxx")
-        except ImportError:
+        except (ImportError, RuntimeError):
             skip("gmpxx not installed")
 
         assert cppjit.gbl.std.vector[cppjit.gbl.mpz_class].value_type
diff --git a/test/test_stltypes.py b/test/test_stltypes.py
index 72d0a21..ad6fdbd 100644
--- a/test/test_stltypes.py
+++ b/test/test_stltypes.py
@@ -4,7 +4,6 @@
 import py
 from pytest import mark, raises, skip
 from support import (
-    IS_CLANG_DEBUG,
     IS_CLANG_REPL,
     IS_CLING,
     IS_LINUX_ARM,
@@ -1839,10 +1838,6 @@ def test01_string_through_string_view(self):
         assert countit(v) == 4
         assert countit_cr(v) == 4
 
-    @mark.xfail(
-        run=not (IS_CLANG_DEBUG or IS_CLING),
-        reason="Crashes on ClangRepl with 'toString not implemented', and on Cling",
-    )
     def test02_string_view_from_unicode(self):
         """Life-time management of converted unicode strings"""