diff --git a/mlir/tools/mlir-tblgen/PassGen.cpp b/mlir/tools/mlir-tblgen/PassGen.cpp
--- a/mlir/tools/mlir-tblgen/PassGen.cpp
+++ b/mlir/tools/mlir-tblgen/PassGen.cpp
@@ -192,7 +192,7 @@
 /// {1}: The base class for the pass.
 /// {2): The command line argument for the pass.
 /// {3}: The dependent dialects registration.
-const char *const passDeclBegin = R"(
+const char *const baseClassBegin = R"(
 template <typename DerivedT>
 class {0}Base : public {1} {
 public:
@@ -243,18 +243,42 @@
   registry.insert<{0}>();
 )";
 
-const char *const friendDefaultConstructorTemplate = R"(
+const char *const friendDefaultConstructorDeclTemplate = R"(
+namespace impl {{
+  std::unique_ptr<::mlir::Pass> create{0}();
+} // namespace impl
+)";
+
+const char *const friendDefaultConstructorWithOptionsDeclTemplate = R"(
+namespace impl {{
+  std::unique_ptr<::mlir::Pass> create{0}(const {0}Options &options);
+} // namespace impl
+)";
+
+const char *const friendDefaultConstructorDefTemplate = R"(
   friend std::unique_ptr<::mlir::Pass> create{0}() {{
     return std::make_unique<DerivedT>();
   }
 )";
 
-const char *const friendDefaultConstructorWithOptionsTemplate = R"(
+const char *const friendDefaultConstructorWithOptionsDefTemplate = R"(
   friend std::unique_ptr<::mlir::Pass> create{0}(const {0}Options &options) {{
     return std::make_unique<DerivedT>(options);
   }
 )";
 
+const char *const defaultConstructorDefTemplate = R"(
+std::unique_ptr<::mlir::Pass> create{0}() {{
+  return impl::create{0}();
+}
+)";
+
+const char *const defaultConstructorWithOptionsDefTemplate = R"(
+std::unique_ptr<::mlir::Pass> create{0}(const {0}Options &options) {{
+  return impl::create{0}(options);
+}
+)";
+
 /// Emit the declarations for each of the pass options.
 static void emitPassOptionDecls(const Pass &pass, raw_ostream &os) {
   for (const PassOption &opt : pass.getOptions()) {
@@ -285,10 +309,20 @@
 static void emitPassDefs(const Pass &pass, raw_ostream &os) {
   StringRef passName = pass.getDef()->getName();
   std::string enableVarName = "GEN_PASS_DEF_" + passName.upper();
+  bool emitDefaultConstructors = pass.getConstructor().empty();
+  bool emitDefaultConstructorWithOptions = !pass.getOptions().empty();
 
   os << "#ifdef " << enableVarName << "\n";
   os << llvm::formatv(passHeader, passName);
 
+  if (emitDefaultConstructors) {
+    os << llvm::formatv(friendDefaultConstructorDeclTemplate, passName);
+
+    if (emitDefaultConstructorWithOptions)
+      os << llvm::formatv(friendDefaultConstructorWithOptionsDeclTemplate,
+                          passName);
+  }
+
   std::string dependentDialectRegistrations;
   {
     llvm::raw_string_ostream dialectsOs(dependentDialectRegistrations);
@@ -297,7 +331,8 @@
                                   dependentDialect);
   }
 
-  os << llvm::formatv(passDeclBegin, passName, pass.getBaseClass(),
+  os << "namespace impl {\n";
+  os << llvm::formatv(baseClassBegin, passName, pass.getBaseClass(),
                       pass.getArgument(), pass.getSummary(),
                       dependentDialectRegistrations);
 
@@ -320,15 +355,23 @@
   // Private content
   os << "private:\n";
 
-  if (pass.getConstructor().empty()) {
-    os << llvm::formatv(friendDefaultConstructorTemplate, passName);
+  if (emitDefaultConstructors) {
+    os << llvm::formatv(friendDefaultConstructorDefTemplate, passName);
 
     if (!pass.getOptions().empty())
-      os << llvm::formatv(friendDefaultConstructorWithOptionsTemplate,
+      os << llvm::formatv(friendDefaultConstructorWithOptionsDefTemplate,
                           passName);
   }
 
   os << "};\n";
+  os << "} // namespace impl\n";
+
+  if (emitDefaultConstructors) {
+    os << llvm::formatv(defaultConstructorDefTemplate, passName);
+
+    if (emitDefaultConstructorWithOptions)
+      os << llvm::formatv(defaultConstructorWithOptionsDefTemplate, passName);
+  }
 
   os << "#undef " << enableVarName << "\n";
   os << "#endif // " << enableVarName << "\n";
diff --git a/mlir/unittests/TableGen/PassGenTest.cpp b/mlir/unittests/TableGen/PassGenTest.cpp
--- a/mlir/unittests/TableGen/PassGenTest.cpp
+++ b/mlir/unittests/TableGen/PassGenTest.cpp
@@ -24,7 +24,7 @@
 #define GEN_PASS_DEF_TESTPASSWITHCUSTOMCONSTRUCTOR
 #include "PassGenTest.cpp.inc"
 
-struct TestPass : public TestPassBase<TestPass> {
+struct TestPass : public impl::TestPassBase<TestPass> {
   using TestPassBase::TestPassBase;
 
   void runOnOperation() override {}
@@ -54,7 +54,7 @@
 }
 
 struct TestPassWithOptions
-    : public TestPassWithOptionsBase<TestPassWithOptions> {
+    : public impl::TestPassWithOptionsBase<TestPassWithOptions> {
   using TestPassWithOptionsBase::TestPassWithOptionsBase;
 
   void runOnOperation() override {}
@@ -89,7 +89,8 @@
 }
 
 struct TestPassWithCustomConstructor
-    : public TestPassWithCustomConstructorBase<TestPassWithCustomConstructor> {
+    : public impl::TestPassWithCustomConstructorBase<
+          TestPassWithCustomConstructor> {
   explicit TestPassWithCustomConstructor(int v) : extraVal(v) {}
 
   void runOnOperation() override {}