diff --git a/mlir/lib/Dialect/Arith/Transforms/EmulateUnsupportedFloats.cpp b/mlir/lib/Dialect/Arith/Transforms/EmulateUnsupportedFloats.cpp
--- a/mlir/lib/Dialect/Arith/Transforms/EmulateUnsupportedFloats.cpp
+++ b/mlir/lib/Dialect/Arith/Transforms/EmulateUnsupportedFloats.cpp
@@ -19,6 +19,7 @@
 #include "mlir/IR/PatternMatch.h"
 #include "mlir/Transforms/DialectConversion.h"
 #include "llvm/ADT/STLExtras.h"
+#include "llvm/Support/ErrorHandling.h"
 #include <optional>
 
 namespace mlir::arith {
@@ -81,8 +82,13 @@
   Location loc = op->getLoc();
   TypeConverter *converter = getTypeConverter();
   SmallVector<Type> resultTypes;
-  LogicalResult pass = converter->convertTypes(op->getResultTypes(), resultTypes);
-  (void) pass;
+  LogicalResult didConvert =
+      converter->convertTypes(op->getResultTypes(), resultTypes);
+  if (failed(didConvert)) {
+    op->emitOpError(
+        "type conversion failed in float emulation, this can't happen");
+    return;
+  }
   Operation *expandedOp =
       rewriter.create(loc, op->getName().getIdentifier(), operands, resultTypes,
                       op->getAttrs(), op->getSuccessors(), /*regions=*/{});