diff --git a/mlir/lib/Conversion/FuncToLLVM/FuncToLLVM.cpp b/mlir/lib/Conversion/FuncToLLVM/FuncToLLVM.cpp
index 55f0a9ac3bbb2..328c605add65c 100644
--- a/mlir/lib/Conversion/FuncToLLVM/FuncToLLVM.cpp
+++ b/mlir/lib/Conversion/FuncToLLVM/FuncToLLVM.cpp
@@ -320,13 +320,22 @@ mlir::convertFuncOpToLLVMFuncOp(FunctionOpInterface funcOp,
   // overriden with an LLVM pointer type for later processing.
   SmallVector<std::optional<NamedAttribute>> byValRefNonPtrAttrs;
   TypeConverter::SignatureConversion result(funcOp.getNumArguments());
-  auto llvmType = converter.convertFunctionSignature(
-      funcOp, varargsAttr && varargsAttr.getValue(),
-      shouldUseBarePtrCallConv(funcOp, &converter), result,
-      byValRefNonPtrAttrs);
+  auto llvmType = dyn_cast_or_null<LLVM::LLVMFunctionType>(
+      converter.convertFunctionSignature(
+          funcOp, varargsAttr && varargsAttr.getValue(),
+          shouldUseBarePtrCallConv(funcOp, &converter), result,
+          byValRefNonPtrAttrs));
   if (!llvmType)
     return rewriter.notifyMatchFailure(funcOp, "signature conversion failed");
 
+  // Check for unsupported variadic functions.
+  if (!shouldUseBarePtrCallConv(funcOp, &converter))
+    if (funcOp->getAttrOfType<UnitAttr>(
+            LLVM::LLVMDialect::getEmitCWrapperAttrName()))
+      if (llvmType.isVarArg())
+        return funcOp.emitError("C interface for variadic functions is not "
+                                "supported yet.");
+
   // Create an LLVM function, use external linkage by default until MLIR
   // functions have linkage.
   LLVM::Linkage linkage = LLVM::Linkage::External;
@@ -342,6 +351,18 @@ mlir::convertFuncOpToLLVMFuncOp(FunctionOpInterface funcOp,
     linkage = attr.getLinkage();
   }
 
+  // Check for invalid attributes.
+  StringRef readnoneAttrName = LLVM::LLVMDialect::getReadnoneAttrName();
+  if (funcOp->hasAttr(readnoneAttrName)) {
+    auto attr = funcOp->getAttrOfType<UnitAttr>(readnoneAttrName);
+    if (!attr) {
+      funcOp->emitError() << "Contains " << readnoneAttrName
+                          << " attribute not of type UnitAttr";
+      return rewriter.notifyMatchFailure(
+          funcOp, "Contains readnone attribute not of type UnitAttr");
+    }
+  }
+
   SmallVector<NamedAttribute, 4> attributes;
   filterFuncAttributes(funcOp, attributes);
   auto newFuncOp = rewriter.create<LLVM::LLVMFuncOp>(
@@ -352,15 +373,7 @@ mlir::convertFuncOpToLLVMFuncOp(FunctionOpInterface funcOp,
       .setVisibility(funcOp.getVisibility());
 
   // Create a memory effect attribute corresponding to readnone.
-  StringRef readnoneAttrName = LLVM::LLVMDialect::getReadnoneAttrName();
   if (funcOp->hasAttr(readnoneAttrName)) {
-    auto attr = funcOp->getAttrOfType<UnitAttr>(readnoneAttrName);
-    if (!attr) {
-      funcOp->emitError() << "Contains " << readnoneAttrName
-                          << " attribute not of type UnitAttr";
-      return rewriter.notifyMatchFailure(
-          funcOp, "Contains readnone attribute not of type UnitAttr");
-    }
     auto memoryAttr = LLVM::MemoryEffectsAttr::get(
         rewriter.getContext(),
         {LLVM::ModRefInfo::NoModRef, LLVM::ModRefInfo::NoModRef,
@@ -447,10 +460,6 @@ mlir::convertFuncOpToLLVMFuncOp(FunctionOpInterface funcOp,
   if (!shouldUseBarePtrCallConv(funcOp, &converter)) {
     if (funcOp->getAttrOfType<UnitAttr>(
             LLVM::LLVMDialect::getEmitCWrapperAttrName())) {
-      if (newFuncOp.isVarArg())
-        return funcOp.emitError("C interface for variadic functions is not "
-                                "supported yet.");
-
       if (newFuncOp.isExternal())
         wrapExternalFunction(rewriter, funcOp->getLoc(), converter, funcOp,
                              newFuncOp);