diff --git a/clang/include/clang/AST/ASTImporter.h b/clang/include/clang/AST/ASTImporter.h
--- a/clang/include/clang/AST/ASTImporter.h
+++ b/clang/include/clang/AST/ASTImporter.h
@@ -378,6 +378,20 @@
     /// imported. If it does not exist nullptr is returned.
     TranslationUnitDecl *GetFromTU(Decl *ToD);
 
+    /// Return the declaration in the "from" context from which the declaration
+    /// in the "to" context was imported. If it was not imported or of the wrong
+    /// type a null value is returned.
+    template <typename DeclT>
+    llvm::Optional<DeclT *> getImportedFromDecl(const DeclT *ToD) const {
+      auto FromI = ImportedFromDecls.find(ToD);
+      if (FromI == ImportedFromDecls.end())
+        return {};
+      auto *FromD = dyn_cast<DeclT>(FromI->second);
+      if (!FromD)
+        return {};
+      return FromD;
+    }
+
     /// Import the given declaration context from the "from"
     /// AST context into the "to" AST context.
     ///
diff --git a/clang/lib/AST/ASTImporter.cpp b/clang/lib/AST/ASTImporter.cpp
--- a/clang/lib/AST/ASTImporter.cpp
+++ b/clang/lib/AST/ASTImporter.cpp
@@ -426,6 +426,9 @@
 
     Error ImportFunctionDeclBody(FunctionDecl *FromFD, FunctionDecl *ToFD);
 
+    Error ImportDefaultArgOfParmVarDecl(const ParmVarDecl *FromParam,
+                                        ParmVarDecl *ToParam);
+
     template <typename T>
     bool hasSameVisibilityContext(T *Found, T *From);
 
@@ -3841,6 +3844,28 @@
   return ToParm;
 }
 
+Error ASTNodeImporter::ImportDefaultArgOfParmVarDecl(
+    const ParmVarDecl *FromParam, ParmVarDecl *ToParam) {
+  ToParam->setHasInheritedDefaultArg(FromParam->hasInheritedDefaultArg());
+  ToParam->setKNRPromoted(FromParam->isKNRPromoted());
+
+  if (FromParam->hasUninstantiatedDefaultArg()) {
+    if (auto ToDefArgOrErr = import(FromParam->getUninstantiatedDefaultArg()))
+      ToParam->setUninstantiatedDefaultArg(*ToDefArgOrErr);
+    else
+      return ToDefArgOrErr.takeError();
+  } else if (FromParam->hasUnparsedDefaultArg()) {
+    ToParam->setUnparsedDefaultArg();
+  } else if (FromParam->hasDefaultArg()) {
+    if (auto ToDefArgOrErr = import(FromParam->getDefaultArg()))
+      ToParam->setDefaultArg(*ToDefArgOrErr);
+    else
+      return ToDefArgOrErr.takeError();
+  }
+
+  return Error::success();
+}
+
 ExpectedDecl ASTNodeImporter::VisitParmVarDecl(ParmVarDecl *D) {
   // Parameters are created in the translation unit's context, then moved
   // into the function declaration's context afterward.
@@ -3867,23 +3892,11 @@
                               /*DefaultArg*/ nullptr))
     return ToParm;
 
-  // Set the default argument.
-  ToParm->setHasInheritedDefaultArg(D->hasInheritedDefaultArg());
-  ToParm->setKNRPromoted(D->isKNRPromoted());
-
-  if (D->hasUninstantiatedDefaultArg()) {
-    if (auto ToDefArgOrErr = import(D->getUninstantiatedDefaultArg()))
-      ToParm->setUninstantiatedDefaultArg(*ToDefArgOrErr);
-    else
-      return ToDefArgOrErr.takeError();
-  } else if (D->hasUnparsedDefaultArg()) {
-    ToParm->setUnparsedDefaultArg();
-  } else if (D->hasDefaultArg()) {
-    if (auto ToDefArgOrErr = import(D->getDefaultArg()))
-      ToParm->setDefaultArg(*ToDefArgOrErr);
-    else
-      return ToDefArgOrErr.takeError();
-  }
+  // Set the default argument. It should be no problem if it was already done.
+  // Do not import the default expression before GetImportedOrCreateDecl call
+  // to avoid possible infinite import loop because circular dependency.
+  if (Error Err = ImportDefaultArgOfParmVarDecl(D, ToParm))
+    return std::move(Err);
 
   if (D->isObjCMethodParameter()) {
     ToParm->setObjCMethodScopeInfo(D->getFunctionScopeIndex());
@@ -6939,8 +6952,23 @@
   if (!UsedContextOrErr)
     return UsedContextOrErr.takeError();
 
-  return CXXDefaultArgExpr::Create(
-      Importer.getToContext(), *ToUsedLocOrErr, *ToParamOrErr, *UsedContextOrErr);
+  // Import the default arg if it was not imported yet.
+  // This is needed because it can happen that during the import of the
+  // default expression (from VisitParmVarDecl) the same ParmVarDecl is
+  // encountered here. The default argument for a ParmVarDecl is set in the
+  // ParmVarDecl only after it is imported (set in VisitParmVarDecl if not here,
+  // see VisitParmVarDecl).
+  ParmVarDecl *ToParam = *ToParamOrErr;
+  if (!ToParam->getDefaultArg()) {
+    Optional<ParmVarDecl *> FromParam = Importer.getImportedFromDecl(ToParam);
+    assert(FromParam && "ParmVarDecl was not imported?");
+
+    if (Error Err = ImportDefaultArgOfParmVarDecl(*FromParam, ToParam))
+      return std::move(Err);
+  }
+
+  return CXXDefaultArgExpr::Create(Importer.getToContext(), *ToUsedLocOrErr,
+                                   *ToParamOrErr, *UsedContextOrErr);
 }
 
 ExpectedStmt
diff --git a/clang/test/Analysis/Inputs/ctu-other.cpp b/clang/test/Analysis/Inputs/ctu-other.cpp
--- a/clang/test/Analysis/Inputs/ctu-other.cpp
+++ b/clang/test/Analysis/Inputs/ctu-other.cpp
@@ -145,3 +145,22 @@
   static const int Test;
 };
 const int TestAnonUnionUSR::Test = 5;
+
+struct DefaultParmContext {
+  static const int I;
+  int f();
+};
+
+int fDefaultParm(int I = DefaultParmContext::I) {
+  return I;
+}
+
+int testImportOfIncompleteDefaultParmDuringImport(int I) {
+  return fDefaultParm(I);
+}
+
+const int DefaultParmContext::I = 0;
+
+int DefaultParmContext::f() {
+  return fDefaultParm();
+}
diff --git a/clang/test/Analysis/Inputs/ctu-other.cpp.externalDefMap.txt b/clang/test/Analysis/Inputs/ctu-other.cpp.externalDefMap.txt
--- a/clang/test/Analysis/Inputs/ctu-other.cpp.externalDefMap.txt
+++ b/clang/test/Analysis/Inputs/ctu-other.cpp.externalDefMap.txt
@@ -26,3 +26,4 @@
 c:@extSCC ctu-other.cpp.ast
 c:@extU ctu-other.cpp.ast
 c:@S@TestAnonUnionUSR@Test ctu-other.cpp.ast
+c:@F@testImportOfIncompleteDefaultParmDuringImport#I# ctu-other.cpp.ast
diff --git a/clang/test/Analysis/ctu-main.cpp b/clang/test/Analysis/ctu-main.cpp
--- a/clang/test/Analysis/ctu-main.cpp
+++ b/clang/test/Analysis/ctu-main.cpp
@@ -125,6 +125,8 @@
   static const int Test;
 };
 
+extern int testImportOfIncompleteDefaultParmDuringImport(int);
+
 int main() {
   clang_analyzer_eval(f(3) == 2); // expected-warning{{TRUE}}
   clang_analyzer_eval(f(4) == 3); // expected-warning{{TRUE}}
@@ -157,5 +159,8 @@
   clang_analyzer_eval(extSubSCN.a == 1); // expected-warning{{TRUE}}
   // clang_analyzer_eval(extSCC.a == 7); // TODO
   clang_analyzer_eval(extU.a == 4); // expected-warning{{TRUE}}
+
   clang_analyzer_eval(TestAnonUnionUSR::Test == 5); // expected-warning{{TRUE}}
+
+  clang_analyzer_eval(testImportOfIncompleteDefaultParmDuringImport(9) == 9); // expected-warning{{TRUE}}
 }