diff --git a/include/swift/AST/SubstitutionMap.h b/include/swift/AST/SubstitutionMap.h
index fa883df80b080..2f3549fabf6ba 100644
--- a/include/swift/AST/SubstitutionMap.h
+++ b/include/swift/AST/SubstitutionMap.h
@@ -286,6 +286,12 @@ class SubstitutionMap {
   Type lookupSubstitution(CanSubstitutableType type) const;
 };
 
+inline llvm::raw_ostream &operator<<(llvm::raw_ostream &OS,
+                                     const SubstitutionMap &subs) {
+  subs.dump(OS);
+  return OS;
+}
+
 /// A function object suitable for use as a \c TypeSubstitutionFn that
 /// queries an underlying \c SubstitutionMap.
 struct QuerySubstitutionMap {