diff --git a/mlir/lib/IR/AsmPrinter.cpp b/mlir/lib/IR/AsmPrinter.cpp
--- a/mlir/lib/IR/AsmPrinter.cpp
+++ b/mlir/lib/IR/AsmPrinter.cpp
@@ -1490,6 +1490,11 @@
 }
 
 void ModulePrinter::printType(Type type) {
+  if (!type) {
+    os << "<<NULL TYPE>>";
+    return;
+  }
+
   // Check for an alias for this type.
   if (state) {
     StringRef alias = state->getAliasState().getTypeAlias(type);