diff --git a/internal/workflowfile/testdata/mixed_refs.yml b/internal/workflowfile/testdata/mixed_refs.yml
index 5a86a329..7077d318 100644
--- a/internal/workflowfile/testdata/mixed_refs.yml
+++ b/internal/workflowfile/testdata/mixed_refs.yml
@@ -8,7 +8,6 @@ jobs:
       - uses: ./local-action
       - uses: docker://alpine:3.18
       - uses: actions/cache/save@v4
-      - uses: ${{ matrix.action }}
       - uses: owner/repo/.github/workflows/called.yml@v1
       - uses: owner/repo/.github/workflows/called.yaml@main
       - uses: actions/setup-node@v4
diff --git a/internal/workflowfile/workflowfile.go b/internal/workflowfile/workflowfile.go
index ea4c8cf5..cda5aeb9 100644
--- a/internal/workflowfile/workflowfile.go
+++ b/internal/workflowfile/workflowfile.go
@@ -48,9 +48,34 @@ func Parse(path string, content []byte) (*File, error) {
 		return nil, fmt.Errorf("parsing workflow YAML: %w", err)
 	}
 
+	var invalid []string
+	walkUses(&f.root, func(value string, _ bool) {
+		if isUsesExpression(value) {
+			invalid = append(invalid, strings.TrimSpace(value))
+		}
+	})
+	if len(invalid) > 0 {
+		return nil, usesExpressionErr(invalid)
+	}
+
 	return f, nil
 }
 
+// isUsesExpression reports whether a `uses:` value contains an expression.
+// Malformed `$/…@ref` values are excluded so the more specific self
+// repository diagnostic still wins.
+func isUsesExpression(value string) bool {
+	value = strings.TrimSpace(value)
+	return strings.Contains(value, "${") && !SelfRepositoryRefHasVersion(value)
+}
+
+// usesExpressionErr reports an expression in `uses:`. GitHub Actions rejects
+// the workflow outright at both step and job level (no context is in scope
+// there), so parsing fails rather than skipping the line.
+func usesExpressionErr(values []string) error {
+	return fmt.Errorf("`uses:` can't contain an expression: %s", strings.Join(values, ", "))
+}
+
 // RefScan is the classified result of walking a workflow's `uses:` values.
 type RefScan struct {
 	// Refs are remote repository action references (owner/repo[/path]@ref).
@@ -88,10 +113,6 @@ func (f *File) ExtractActionRefs() RefScan {
 			}
 			return
 		}
-		if strings.Contains(value, "${") {
-			scan.Warnings = append(scan.Warnings, fmt.Sprintf("skipping unparseable uses: value %q (expressions are not supported)", value))
-			return
-		}
 		if IsSelfRepositoryAction(value) {
 			// Bare `$/…` is a legal self repository reference at both step level
 			// (action dir) and job level (reusable-workflow file): "this repo
@@ -212,8 +233,6 @@ func ScanSelfRepositoryActions(workflowPath string, actionRefs []string) SelfRep
 					seenInvalid[use] = true
 					scan.SelfRepositoryRefErrs = append(scan.SelfRepositoryRefErrs, use)
 				}
-			case strings.Contains(use, "${"):
-				scan.Warnings = append(scan.Warnings, fmt.Sprintf("skipping unparseable uses: value %q in %s (expressions are not supported)", use, current.ref))
 			case IsSelfRepositoryAction(use):
 				if !seenSelf[use] {
 					seenSelf[use] = true
@@ -375,37 +394,81 @@ func ExtractLocalCompositeRefs(workflowPath string, localPaths []string) ([]pars
 	return refs, warnings
 }
 
+// walkUses visits `uses:` values at the only places GitHub Actions honors
+// them: `jobs.<id>.uses`, `jobs.<id>.steps[*].uses` in a workflow, and
+// `runs.steps[*].uses` in a composite action definition. A `uses` key
+// anywhere else (an env var, a `with:` input) is ordinary data, not a
+// reference.
 func walkUses(node *yaml.Node, fn func(value string, stepLevel bool)) {
-	walkUsesDepth(node, false, fn, 0)
+	root := resolveAlias(documentRoot(node))
+	walkStepUses(mapValue(root, "runs"), fn)
+
+	jobs := mapValue(root, "jobs")
+	if jobs == nil || jobs.Kind != yaml.MappingNode {
+		return
+	}
+	for i := 1; i < len(jobs.Content); i += 2 {
+		job := resolveAlias(jobs.Content[i])
+		if job == nil || job.Kind != yaml.MappingNode {
+			continue
+		}
+		if use := scalarValue(mapValue(job, "uses")); use != "" {
+			fn(use, false)
+		}
+		walkStepUses(job, fn)
+	}
 }
 
-func walkUsesDepth(node *yaml.Node, inStep bool, fn func(value string, stepLevel bool), depth int) {
-	if node == nil || depth > maxYAMLWalkDepth {
+// walkStepUses visits the `uses:` of each step in owner's `steps:` sequence.
+func walkStepUses(owner *yaml.Node, fn func(value string, stepLevel bool)) {
+	steps := mapValue(owner, "steps")
+	if steps == nil || steps.Kind != yaml.SequenceNode {
 		return
 	}
-	switch node.Kind {
-	case yaml.DocumentNode, yaml.SequenceNode:
-		for _, child := range node.Content {
-			walkUsesDepth(child, inStep, fn, depth+1)
+	for _, stepNode := range steps.Content {
+		step := resolveAlias(stepNode)
+		if step == nil || step.Kind != yaml.MappingNode {
+			continue
 		}
-	case yaml.MappingNode:
-		for i := 0; i < len(node.Content)-1; i += 2 {
-			key := node.Content[i]
-			value := node.Content[i+1]
-			childInStep := inStep
-			if key.Kind == yaml.ScalarNode {
-				switch key.Value {
-				case "uses":
-					if value.Kind == yaml.ScalarNode {
-						fn(value.Value, inStep)
-					}
-				case "steps":
-					childInStep = true
-				}
-			}
-			walkUsesDepth(value, childInStep, fn, depth+1)
+		if use := scalarValue(mapValue(step, "uses")); use != "" {
+			fn(use, true)
+		}
+	}
+}
+
+func documentRoot(node *yaml.Node) *yaml.Node {
+	if node != nil && node.Kind == yaml.DocumentNode && len(node.Content) > 0 {
+		return node.Content[0]
+	}
+	return node
+}
+
+// resolveAlias dereferences YAML anchors so an aliased job or step is walked
+// like the node it points at.
+func resolveAlias(node *yaml.Node) *yaml.Node {
+	for i := 0; node != nil && node.Kind == yaml.AliasNode && i < maxYAMLWalkDepth; i++ {
+		node = node.Alias
+	}
+	return node
+}
+
+func mapValue(node *yaml.Node, key string) *yaml.Node {
+	if node == nil || node.Kind != yaml.MappingNode {
+		return nil
+	}
+	for i := 0; i < len(node.Content)-1; i += 2 {
+		if node.Content[i].Kind == yaml.ScalarNode && node.Content[i].Value == key {
+			return resolveAlias(node.Content[i+1])
 		}
 	}
+	return nil
+}
+
+func scalarValue(node *yaml.Node) string {
+	if node == nil || node.Kind != yaml.ScalarNode {
+		return ""
+	}
+	return node.Value
 }
 
 // maxYAMLWalkDepth bounds recursion in walkYAMLNodes so a hostile or
@@ -517,11 +580,19 @@ func parseActionYAMLForUses(content []byte) ([]string, error) {
 	}
 
 	var uses []string
+	var invalid []string
 	for _, step := range action.Runs.Steps {
-		if step.Uses != "" {
+		switch {
+		case step.Uses == "":
+		case isUsesExpression(step.Uses):
+			invalid = append(invalid, strings.TrimSpace(step.Uses))
+		default:
 			uses = append(uses, step.Uses)
 		}
 	}
+	if len(invalid) > 0 {
+		return nil, usesExpressionErr(invalid)
+	}
 	return uses, nil
 }
 
diff --git a/internal/workflowfile/workflowfile_test.go b/internal/workflowfile/workflowfile_test.go
index 4597e6b1..e0b2a9b4 100644
--- a/internal/workflowfile/workflowfile_test.go
+++ b/internal/workflowfile/workflowfile_test.go
@@ -41,9 +41,32 @@ func TestExtractActionRefsMixed(t *testing.T) {
 
 	assert.Len(t, localPaths, 1)
 	assert.Equal(t, "./local-action", localPaths[0])
+	assert.Empty(t, warnings)
+}
 
-	assert.Len(t, warnings, 1)
-	assert.Contains(t, warnings[0], "unparseable uses:")
+func TestParseRejectsUsesExpression(t *testing.T) {
+	for name, content := range map[string]string{
+		"step level": `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: ${{ format('actions/checkout@v4') }}
+`,
+		"job level": `
+on: push
+jobs:
+  call:
+    uses: owner/repo/.github/workflows/x.yml@${{ github.ref_name }}
+`,
+	} {
+		t.Run(name, func(t *testing.T) {
+			_, err := Parse("wf.yml", []byte(content))
+			require.Error(t, err)
+			assert.Contains(t, err.Error(), "`uses:` can't contain an expression")
+		})
+	}
 }
 
 func TestExtractActionRefs_SelfRepositoryClassification(t *testing.T) {
@@ -382,3 +405,52 @@ func TestExtractLocalCompositeRefs_RejectsPathTraversal(t *testing.T) {
 	}
 	assert.True(t, sawRefusal, "expected refusal warning, got: %#v", warnings)
 }
+
+func TestParseIgnoresNonUsesKeys(t *testing.T) {
+	f, err := Parse("wf.yml", []byte(`
+on: push
+env:
+  uses: ${{ github.repository }}
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          uses: ${{ github.ref }}
+`))
+	require.NoError(t, err)
+	assert.Len(t, f.ExtractActionRefs().Refs, 1)
+}
+
+func TestParseRejectsAliasedUsesExpression(t *testing.T) {
+	_, err := Parse("wf.yml", []byte(`
+on: push
+x: &step
+  uses: ${{ matrix.action }}
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - *step
+`))
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "`uses:` can't contain an expression")
+}
+
+func TestScanSelfRepositoryActionsRejectsUsesExpression(t *testing.T) {
+	root := t.TempDir()
+	require.NoError(t, os.MkdirAll(filepath.Join(root, ".git"), 0o755))
+	require.NoError(t, os.MkdirAll(filepath.Join(root, "actions", "compo"), 0o755))
+	require.NoError(t, os.WriteFile(filepath.Join(root, "actions", "compo", "action.yml"), []byte(`
+runs:
+  using: composite
+  steps:
+    - uses: actions/checkout@${{ inputs.ref }}
+`), 0o644))
+
+	scan := ScanSelfRepositoryActions(filepath.Join(root, ".github", "workflows", "ci.yml"), []string{"$/actions/compo"})
+	require.Len(t, scan.Errors, 1)
+	assert.Contains(t, scan.Errors[0], "`uses:` can't contain an expression")
+	assert.Empty(t, scan.Refs)
+}
diff --git a/test/scenarios/catalog.yml b/test/scenarios/catalog.yml
index 886bfe0a..1238875b 100644
--- a/test/scenarios/catalog.yml
+++ b/test/scenarios/catalog.yml
@@ -414,8 +414,9 @@ scenarios:
 
   - name: expression_in_uses
     category: workflow_parsing
-    description: "Expression-based uses: (${{ }}) — unparseable, skipped with warning"
-    needs_token: true
+    description: "Expression-based uses: (${{ }}) — illegal in Actions, fails to parse"
+    needs_stub: true
+    tags: [stub]
     fixtures:
       workflows:
         ci.yml:
@@ -429,8 +430,8 @@ scenarios:
                   - uses: ${{ matrix.action }}
                   - uses: actions/checkout@v4
     expect:
-      exit: 0
-      lockfile_deps_cover_direct: true
+      exit: 2
+      output_contains: ["can't contain an expression"]
 
   - name: local_action_skipped
     category: workflow_parsing