diff --git a/mlir/lib/Conversion/StandardToLLVM/StandardToLLVM.cpp b/mlir/lib/Conversion/StandardToLLVM/StandardToLLVM.cpp
--- a/mlir/lib/Conversion/StandardToLLVM/StandardToLLVM.cpp
+++ b/mlir/lib/Conversion/StandardToLLVM/StandardToLLVM.cpp
@@ -1110,6 +1110,8 @@
     TypeConverter::SignatureConversion result(funcOp.getNumArguments());
     auto llvmType = typeConverter.convertFunctionSignature(
         funcOp.getType(), varargsAttr && varargsAttr.getValue(), result);
+    if (!llvmType)
+      return nullptr;
 
     // Propagate argument attributes to all converted arguments obtained after
     // converting a given original argument.
diff --git a/mlir/test/Conversion/StandardToLLVM/invalid.mlir b/mlir/test/Conversion/StandardToLLVM/invalid.mlir
--- a/mlir/test/Conversion/StandardToLLVM/invalid.mlir
+++ b/mlir/test/Conversion/StandardToLLVM/invalid.mlir
@@ -29,3 +29,8 @@
   %1 = llvm.mlir.cast %0 : vector<1x1xf32> to !llvm.vec<1 x float>
   return %1 : !llvm.vec<1 x float>
 }
+
+// -----
+
+// Should not crash on unsupported types in function signatures.
+func @unsupported_signature() -> tensor<10 x i32>