diff --git a/clang/lib/CodeGen/CodeGenAction.cpp b/clang/lib/CodeGen/CodeGenAction.cpp
--- a/clang/lib/CodeGen/CodeGenAction.cpp
+++ b/clang/lib/CodeGen/CodeGenAction.cpp
@@ -779,10 +779,10 @@
     ComputeDiagID(Severity, backend_frame_larger_than, DiagID);
     break;
   case DK_Linker:
-    assert(CurLinkModule);
     // FIXME: stop eating the warnings and notes.
     if (Severity != DS_Error)
       return;
+    assert(CurLinkModule);
     DiagID = diag::err_fe_cannot_link_module;
     break;
   case llvm::DK_OptimizationRemark:
diff --git a/clang/test/CodeGen/Inputs/linker-diagnostic1.ll b/clang/test/CodeGen/Inputs/linker-diagnostic1.ll
new file mode 100644
--- /dev/null
+++ b/clang/test/CodeGen/Inputs/linker-diagnostic1.ll
@@ -0,0 +1,9 @@
+target triple = "armv4-none-unknown-eabi"
+target datalayout = "e-m:e-p:32:32-Fi8-i64:64-v128:64:128-a:0:32-n32-S64"
+
+declare i32 @foo(i32)
+
+define i32 @bar(i32 %x) {
+  %1 = tail call i32 @foo(i32 %x)
+  ret i32 %1
+}
diff --git a/clang/test/CodeGen/linker-diagnostic.ll b/clang/test/CodeGen/linker-diagnostic.ll
new file mode 100644
--- /dev/null
+++ b/clang/test/CodeGen/linker-diagnostic.ll
@@ -0,0 +1,15 @@
+; RUN: mkdir -p %t
+; RUN: opt -module-summary -o %t/foo.o %s
+; RUN: opt -module-summary -o %t/bar.o %S/Inputs/linker-diagnostic1.ll
+; RUN: llvm-lto2 run --thinlto-distributed-indexes -r %t/foo.o,foo,plx -r %t/bar.o,bar,plx \
+; RUN:   -r %t/bar.o,foo, -o %t/foobar.so %t/foo.o %t/bar.o
+; RUN: %clang -c -o %t/lto.bar.o --target=armv6-none-unknown-eabi -O2 \
+; RUN:   -fthinlto-index=%t/bar.o.thinlto.bc %t/bar.o
+
+target triple = "thumbv6-unknown-linux-gnueabihf"
+target datalayout = "e-m:e-p:32:32-Fi8-i64:64-v128:64:128-a:0:32-n32-S64"
+
+define i32 @foo(i32 %x) {
+  %1 = add i32 %x, 1
+  ret i32 %1
+}