diff --git a/pkg/runner/action_composite.go b/pkg/runner/action_composite.go
index 256d36e..9001b48 100644
--- a/pkg/runner/action_composite.go
+++ b/pkg/runner/action_composite.go
@@ -21,6 +21,8 @@ func evaluateCompositeInputAndEnv(ctx context.Context, parent *RunContext, step
 		}
 	}
 
+	ee := parent.NewStepExpressionEvaluator(ctx, step)
+
 	for inputID, input := range step.getActionModel().Inputs {
 		envKey := regexp.MustCompile("[^A-Z0-9-]").ReplaceAllString(strings.ToUpper(inputID), "_")
 		envKey = fmt.Sprintf("INPUT_%s", strings.ToUpper(envKey))
@@ -31,7 +33,8 @@ func evaluateCompositeInputAndEnv(ctx context.Context, parent *RunContext, step
 		if value, ok := stepEnv[envKey]; defined && ok {
 			env[envKey] = value
 		} else {
-			env[envKey] = input.Default
+			// defaults could contain expressions
+			env[envKey] = ee.Interpolate(ctx, input.Default)
 		}
 	}
 
diff --git a/pkg/runner/testdata/uses-composite-with-inputs/action/action.yml b/pkg/runner/testdata/uses-composite-with-inputs/action/action.yml
index 0e35475..82337d5 100644
--- a/pkg/runner/testdata/uses-composite-with-inputs/action/action.yml
+++ b/pkg/runner/testdata/uses-composite-with-inputs/action/action.yml
@@ -5,6 +5,10 @@ inputs:
   some:
     description: "some input"
     required: true
+  other:
+    description: "other input"
+    default: "${{ inputs.some }}"
+    required: false
 outputs:
   out:
     description: "some output"
@@ -17,3 +21,9 @@ runs:
         echo "action input=${{ inputs.some }}"
         [[ "${{ inputs.some == 'value' }}" = "true" ]] || exit 1
       shell: bash
+    - run: |
+        echo "ENV_VAR=$ENV_VAR"
+        [[ "$ENV_VAR" = "value" ]] || exit 1
+      shell: bash
+      env:
+        ENV_VAR: ${{ inputs.other }}