diff --git a/include/clang/Basic/DiagnosticSemaKinds.td b/include/clang/Basic/DiagnosticSemaKinds.td
index 95f6580..4032285 100644
--- a/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/include/clang/Basic/DiagnosticSemaKinds.td
@@ -2299,6 +2299,8 @@
   "conversion to %select{integral|enumeration}0 type %1">;
 def err_switch_explicit_conversion : Error<
   "switch condition type %0 requires explicit conversion to %1">;
+def err_switch_incomplete_class_type : Error<
+  "switch condition has incomplete class type %0">;
 def warn_empty_if_body : Warning<
   "if statement has empty body">, InGroup<EmptyBody>;
 def err_va_start_used_in_non_variadic_function : Error<
diff --git a/lib/Sema/SemaStmt.cpp b/lib/Sema/SemaStmt.cpp
index b674a17..ad3376b 100644
--- a/lib/Sema/SemaStmt.cpp
+++ b/lib/Sema/SemaStmt.cpp
@@ -391,6 +391,13 @@
     // conversion is used in place of the original condition for the remainder
     // of this section. Integral promotions are performed.
     if (!CondExpr->isTypeDependent()) {
+      // Make sure that the condition expression has a complete type,
+      // otherwise we'll never find any conversions.
+      if (RequireCompleteType(SwitchLoc, CondType,
+                              PDiag(diag::err_switch_incomplete_class_type)
+                                << CondExpr->getSourceRange()))
+        return StmtError();
+
       llvm::SmallVector<CXXConversionDecl *, 4> ViableConversions;
       llvm::SmallVector<CXXConversionDecl *, 4> ExplicitConversions;
       if (const RecordType *RecordTy = CondType->getAs<RecordType>()) {
diff --git a/test/SemaCXX/switch.cpp b/test/SemaCXX/switch.cpp
index 2f2f2a9..003d5b8 100644
--- a/test/SemaCXX/switch.cpp
+++ b/test/SemaCXX/switch.cpp
@@ -33,3 +33,10 @@
   switch (B()) { // expected-error{{multiple conversions}}
   }
 }
+
+struct C; // expected-note{{forward declaration}}
+
+void x3(C &c) {
+  switch (c) { // expected-error{{incomplete class type}}
+  }
+}