diff --git a/llvm/lib/Target/AMDGPU/SIISelLowering.cpp b/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
index 70230b5abc517..fc8bbb154d035 100644
--- a/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
+++ b/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
@@ -2537,6 +2537,7 @@ void SITargetLowering::allocatePreloadKernArgSGPRs(
 
       // Arg is preloaded into the previous SGPR.
       if (ArgLoc.getLocVT().getStoreSize() < 4 && Alignment < 4) {
+        assert(InIdx >= 1 && "No previous SGPR");
         Info.getArgInfo().PreloadKernArgs[InIdx].Regs.push_back(
             Info.getArgInfo().PreloadKernArgs[InIdx - 1].Regs[0]);
         continue;