diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -2884,7 +2884,7 @@
     // that are compatible with being a vararg call argument.
     unsigned SRetIdx;
     if (CallerPAL.hasAttrSomewhere(Attribute::StructRet, &SRetIdx) &&
-        SRetIdx > FT->getNumParams())
+        SRetIdx - AttributeList::FirstArgIndex >= FT->getNumParams())
       return false;
   }