Index: COFF/SymbolTable.cpp
===================================================================
--- COFF/SymbolTable.cpp
+++ COFF/SymbolTable.cpp
@@ -347,11 +347,13 @@
       Sym->Body = Body;
       continue;
     }
-    if (auto *L = dyn_cast<Lazy>(Existing)) {
-      // We may see new references to runtime library symbols such as __chkstk
-      // here. These symbols must be wholly defined in non-bitcode files.
-      addMemberFile(L);
-      continue;
+    if (isa<Undefined>(Body)) {
+      if (auto *L = dyn_cast<Lazy>(Existing)) {
+        // We may see new references to runtime library symbols such as __chkstk
+        // here. These symbols must be wholly defined in non-bitcode files.
+        addMemberFile(L);
+        continue;
+      }
     }
 
     int Comp = Existing->compare(Body);
Index: test/COFF/Inputs/lto-lazy-reference-dummy.ll
===================================================================
--- /dev/null
+++ test/COFF/Inputs/lto-lazy-reference-dummy.ll
@@ -0,0 +1,6 @@
+target datalayout = "e-m:x-p:32:32-i64:64-f80:32-n8:16:32-a:0:32-S32"
+target triple = "i686-pc-windows-msvc18.0.0"
+
+define void @dummy() {
+  ret void
+}
Index: test/COFF/Inputs/lto-lazy-reference-quadruple.ll
===================================================================
--- /dev/null
+++ test/COFF/Inputs/lto-lazy-reference-quadruple.ll
@@ -0,0 +1,16 @@
+target datalayout = "e-m:x-p:32:32-i64:64-f80:32-n8:16:32-a:0:32-S32"
+target triple = "i686-pc-windows-msvc18.0.0"
+
+define double @quadruple(double %x) {
+entry:
+  ; The symbol __real@40800000 is used to materialize the 4.0 constant.
+  %mul = fmul double %x, 4.0
+  ret double %mul
+}
+
+
+declare void @dummy()
+define void @f() {
+  call void @dummy()
+  ret void
+}
Index: test/COFF/lto-lazy-reference.ll
===================================================================
--- /dev/null
+++ test/COFF/lto-lazy-reference.ll
@@ -0,0 +1,20 @@
+; RUN: llc -mtriple=i686-pc-windows-msvc -filetype=obj -o %T/lto-lazy-reference-quadruple.obj %S/Inputs/lto-lazy-reference-quadruple.ll
+; RUN: llvm-as -o %T/lto-lazy-reference-dummy.bc %S/Inputs/lto-lazy-reference-dummy.ll
+; RUN: llvm-ar cru %t.lib %T/lto-lazy-reference-quadruple.obj %T/lto-lazy-reference-dummy.bc
+; RUN: llvm-as -o %t.obj %s
+; RUN: lld-link /out:%t.exe /entry:main /subsystem:console %t.obj %t.lib
+
+target datalayout = "e-m:x-p:32:32-i64:64-f80:32-n8:16:32-a:0:32-S32"
+target triple = "i686-pc-windows-msvc18.0.0"
+
+define double @main(double %x) {
+entry:
+  ; When compiled, this defines the __real@40800000 symbol, which already has a
+  ; lazy definition in the lib file from  lto-real-quadruple.obj. This test
+  ; makes sure we *don't* try to take the definition from the lazy reference,
+  ; because that can bring in new references to bitcode files after LTO, such
+  ; as lto-real-dummy.bc in this case.
+  %mul = fmul double %x, 4.0
+
+  ret double %mul
+}