diff --git a/include/swift/AST/ASTContext.h b/include/swift/AST/ASTContext.h
index 80156adc89c..c136634716a 100644
--- a/include/swift/AST/ASTContext.h
+++ b/include/swift/AST/ASTContext.h
@@ -1250,6 +1250,13 @@ public:
   /// in this context.
   void addLoadedModule(ModuleDecl *M);
 
+  /// Remove an externally-sourced module from the set of known loaded modules
+  /// in this context. Modules are added to the cache before being loaded to
+  /// avoid loading a module twice when there is a cyclic dependency between an
+  /// overlay and its Clang module. If a module import fails, the non-imported
+  /// module should be removed from the cache again.
+  void removeLoadedModule(Identifier RealName);
+
   /// Change the behavior of all loaders to ignore swiftmodules next to
   /// swiftinterfaces.
   void setIgnoreAdjacentModules(bool value);
diff --git a/lib/AST/ASTContext.cpp b/lib/AST/ASTContext.cpp
index 01110d8809c..add9e262454 100644
--- a/lib/AST/ASTContext.cpp
+++ b/lib/AST/ASTContext.cpp
@@ -2267,6 +2267,10 @@ void ASTContext::addLoadedModule(ModuleDecl *M) {
   getImpl().LoadedModules[M->getRealName()] = M;
 }
 
+void ASTContext::removeLoadedModule(Identifier RealName) {
+  getImpl().LoadedModules.erase(RealName);
+}
+
 void ASTContext::setIgnoreAdjacentModules(bool value) {
   IgnoreAdjacentModules = value;
 }
diff --git a/lib/Serialization/SerializedModuleLoader.cpp b/lib/Serialization/SerializedModuleLoader.cpp
index f7089856023..3eb0cf981b6 100644
--- a/lib/Serialization/SerializedModuleLoader.cpp
+++ b/lib/Serialization/SerializedModuleLoader.cpp
@@ -1527,12 +1527,16 @@ MemoryBufferSerializedModuleLoader::loadModule(SourceLoc importLoc,
 
   auto *M = ModuleDecl::create(moduleID.Item, Ctx);
   SWIFT_DEFER { M->setHasResolvedImports(); };
+  if (AllowMemoryCache)
+    Ctx.addLoadedModule(M);
 
   auto *file = loadAST(*M, moduleID.Loc, /*moduleInterfacePath=*/"",
                        /*moduleInterfaceSourcePath=*/"",
                        std::move(moduleInputBuffer), {}, {}, isFramework);
-  if (!file)
+  if (!file) {
+    Ctx.removeLoadedModule(moduleID.Item);
     return nullptr;
+  }
 
   // The MemoryBuffer loader is used by LLDB during debugging. Modules imported
   // from .swift_ast sections are never produced from textual interfaces. By
@@ -1540,8 +1544,6 @@ MemoryBufferSerializedModuleLoader::loadModule(SourceLoc importLoc,
   if (BypassResilience)
     M->setBypassResilience();
   M->addFile(*file);
-  if (AllowMemoryCache)
-    Ctx.addLoadedModule(M);
   return M;
 }
 
diff --git a/test/DWARFImporter/basic.swift b/test/DWARFImporter/basic.swift
index a5c30f96495..57490f61dd2 100644
--- a/test/DWARFImporter/basic.swift
+++ b/test/DWARFImporter/basic.swift
@@ -16,9 +16,13 @@
 // RUN: %lldb-moduleimport-test -verbose -dump-module %t/a.out \
 // RUN:    -dummy-dwarfimporter | %FileCheck %s --check-prefix=SWIFTONLY
 
-// CHECK: Importing basic... ok!
-// FAIL: Importing basic... ok!
-// SWIFTONLY: Importing basic... ok!
+// CHECK: Importing basic...
+// CHECK: Import successful!
+// FAIL: Importing basic... 
+// FAIL: Import successful!
+// SWIFTONLY: Importing basic...
+// SWIFTONLY: Import successful!
+
 import ObjCModule
 
 let pureSwift = Int32(42)
diff --git a/test/DebugInfo/ASTSection-multi.swift b/test/DebugInfo/ASTSection-multi.swift
index 3d719608841..1ef3c531de2 100644
--- a/test/DebugInfo/ASTSection-multi.swift
+++ b/test/DebugInfo/ASTSection-multi.swift
@@ -42,8 +42,11 @@
 // RUN:                     %t/a3.o %t/a3-mod.o
 
 // RUN: %lldb-moduleimport-test -verbose %t/a.out | %FileCheck %s
-// CHECK: Importing a0... ok!
-// CHECK: Importing a1... ok!
-// CHECK: Importing a2... ok!
-// CHECK: Importing a3... ok!
+// CHECK-DAG: Importing a0...
+// CHECK-DAG: Import successful!
+// CHECK-DAG: Importing a1...
+// CHECK-DAG: Import successful!
+// CHECK-DAG: Importing a2...
+// CHECK-DAG: Import successful!
+// CHECK-DAG: Importing a3...
 
diff --git a/test/DebugInfo/ASTSection-single.swift b/test/DebugInfo/ASTSection-single.swift
index 11b4fc260d5..ab434c725a8 100644
--- a/test/DebugInfo/ASTSection-single.swift
+++ b/test/DebugInfo/ASTSection-single.swift
@@ -11,4 +11,5 @@
 
 // RUN: %lldb-moduleimport-test -verbose %t/a0-mod.o | %FileCheck %s
 // CHECK: Path: {{.*}}/Inputs, framework=false, system=false
-// CHECK: Importing a0... ok!
+// CHECK: Importing a0...
+// CHECK: Import successful!
diff --git a/test/DebugInfo/ASTSection.swift b/test/DebugInfo/ASTSection.swift
index b55b5faedd3..33fcb54dd88 100644
--- a/test/DebugInfo/ASTSection.swift
+++ b/test/DebugInfo/ASTSection.swift
@@ -26,7 +26,8 @@ func objCUser(_ obj: ObjCClass) {}
 #endif
 
 // CHECK: - Target: {{.+}}-{{.+}}-{{.+}}
-// CHECK: Importing ASTSection... ok!
+// CHECK: Importing ASTSection...
+// CHECK: Import successful!
 
 // LINETABLE-CHECK-NOT: ASTSection
 
diff --git a/test/DebugInfo/ASTSectionOverlay.swift b/test/DebugInfo/ASTSectionOverlay.swift
new file mode 100644
index 00000000000..7c561cc1bf1
--- /dev/null
+++ b/test/DebugInfo/ASTSectionOverlay.swift
@@ -0,0 +1,16 @@
+// REQUIRES: executable_test
+// REQUIRES: objc_interop
+
+// RUN: %empty-directory(%t)
+// RUN: %target-build-swift -emit-module %S/Inputs/overlay.swift -module-name ClangModuleWithOverlay -I %S/Inputs -emit-module-path %t/ClangModuleWithOverlay.swiftmodule
+// RUN: %target-build-swift -c %S/Inputs/overlay.swift -module-name ClangModuleWithOverlay -I %S/Inputs -o %t/ClangModuleWithOverlay.o -parse-as-library
+// RUN: %target-build-swift -emit-executable %s %t/ClangModuleWithOverlay.o -I %t -g -o %t/ASTSectionOverlay -module-name ASTSectionOverlay -emit-module -Xlinker -add_ast_path -Xlinker %t/ClangModuleWithOverlay.swiftmodule
+
+// RUN: %lldb-moduleimport-test -verbose %t/ASTSectionOverlay | %FileCheck %s
+// CHECK: Loading ClangModuleWithOverlay
+// CHECK-NOT: Loading (overlay) ClangModuleWithOverlay
+// CHECK-NOT: Loading{{.*}}ClangModuleWithOverlay
+
+import ClangModuleWithOverlay
+let c = ClangType(i: 0)
+fromSwiftOverlay()
diff --git a/test/DebugInfo/ASTSection_ObjC.swift b/test/DebugInfo/ASTSection_ObjC.swift
index 35f8bf3a885..872c114f06a 100644
--- a/test/DebugInfo/ASTSection_ObjC.swift
+++ b/test/DebugInfo/ASTSection_ObjC.swift
@@ -14,6 +14,7 @@
 // RUN: %lldb-moduleimport-test -verbose %t/ASTSection | %FileCheck %s --allow-empty --check-prefix=LINETABLE-CHECK
 
 // CHECK: - Target: {{.+}}-{{.+}}-{{.+}}
-// CHECK: Importing ASTSection... ok!
+// CHECK: Importing ASTSection...
+// CHECK: Import successful!
 
 // LINETABLE-CHECK-NOT: ASTSection
diff --git a/test/DebugInfo/ASTSection_linker.swift b/test/DebugInfo/ASTSection_linker.swift
index dcf3b9f94ff..cda2450c836 100644
--- a/test/DebugInfo/ASTSection_linker.swift
+++ b/test/DebugInfo/ASTSection_linker.swift
@@ -21,4 +21,6 @@
 // CHECK: - Target: {{.+}}-{{.+}}-{{.+}}
 // CHECK: - SDK path: {{.*}}MacOS{{.*}}.sdk
 // CHECK: - -Xcc options: -working-directory {{.+}} -DA -DB
-// CHECK: Importing ASTSection... ok!
+// CHECK: Importing ASTSection...
+// CHECK: Import successful!
+
diff --git a/test/DebugInfo/Inputs/ClangModuleWithOverlay.h b/test/DebugInfo/Inputs/ClangModuleWithOverlay.h
new file mode 100644
index 00000000000..0957ab6f8cf
--- /dev/null
+++ b/test/DebugInfo/Inputs/ClangModuleWithOverlay.h
@@ -0,0 +1,3 @@
+struct ClangType {
+  int i;
+};
diff --git a/test/DebugInfo/Inputs/module.modulemap b/test/DebugInfo/Inputs/module.modulemap
index 8153b4ecf54..5dd48f36d74 100644
--- a/test/DebugInfo/Inputs/module.modulemap
+++ b/test/DebugInfo/Inputs/module.modulemap
@@ -20,3 +20,7 @@ module Macro {
   header "Macro.h"
 }
 
+module ClangModuleWithOverlay {
+  header "ClangModuleWithOverlay.h"
+  export *
+}
diff --git a/test/DebugInfo/Inputs/overlay.swift b/test/DebugInfo/Inputs/overlay.swift
new file mode 100644
index 00000000000..80ee1ebc66a
--- /dev/null
+++ b/test/DebugInfo/Inputs/overlay.swift
@@ -0,0 +1,3 @@
+@_exported import ClangModuleWithOverlay
+
+public func fromSwiftOverlay() {}
diff --git a/tools/lldb-moduleimport-test/lldb-moduleimport-test.cpp b/tools/lldb-moduleimport-test/lldb-moduleimport-test.cpp
index 3ef93ca99d8..3664f45db48 100644
--- a/tools/lldb-moduleimport-test/lldb-moduleimport-test.cpp
+++ b/tools/lldb-moduleimport-test/lldb-moduleimport-test.cpp
@@ -381,7 +381,25 @@ int main(int argc, char **argv) {
     auto *ClangImporter = static_cast<swift::ClangImporter *>(
         CI.getASTContext().getClangModuleLoader());
     ClangImporter->setDWARFImporterDelegate(dummyDWARFImporter);
-  }
+ }
+
+  if (Verbose)
+    CI.getASTContext().SetPreModuleImportCallback(
+        [&](llvm::StringRef module_name,
+            swift::ASTContext::ModuleImportKind kind) {
+          switch (kind) {
+          case swift::ASTContext::Module:
+            llvm::outs() << "Loading " << module_name.str() << "\n";
+            break;
+          case swift::ASTContext::Overlay:
+            llvm::outs() << "Loading (overlay) " << module_name.str() << "\n";
+            break;
+          case swift::ASTContext::BridgingHeader:
+            llvm::outs() << "Compiling bridging header: " << module_name.str()
+                         << "\n";
+            break;
+          }
+        });
 
   llvm::SmallString<0> error;
   llvm::raw_svector_ostream errs(error);
@@ -401,7 +419,7 @@ int main(int argc, char **argv) {
   // Attempt to import all modules we found.
   for (auto path : modules) {
     if (Verbose)
-      llvm::outs() << "Importing " << path << "... ";
+      llvm::outs() << "Importing " << path << "...\n";
 
     swift::ImportPath::Module::Builder modulePath;
 #ifdef SWIFT_SUPPORTS_SUBMODULES
@@ -420,7 +438,7 @@ int main(int argc, char **argv) {
       return 1;
     }
     if (Verbose)
-      llvm::outs() << "ok!\n";
+      llvm::outs() << "Import successful!\n";
     if (DumpModule) {
       llvm::SmallVector<swift::Decl*, 10> Decls;
       Module->getTopLevelDecls(Decls);