diff --git a/flang/lib/Optimizer/CodeGen/TypeConverter.h b/flang/lib/Optimizer/CodeGen/TypeConverter.h
--- a/flang/lib/Optimizer/CodeGen/TypeConverter.h
+++ b/flang/lib/Optimizer/CodeGen/TypeConverter.h
@@ -60,6 +60,9 @@
         [&](fir::PointerType pointer) { return convertPointerLike(pointer); });
     addConversion(
         [&](fir::RecordType derived) { return convertRecordType(derived); });
+    addConversion([&](fir::LenType field) {
+      return mlir::IntegerType::get(field.getContext(), 32);
+    });
     addConversion(
         [&](fir::ComplexType cmplx) { return convertComplexType(cmplx); });
     addConversion(
diff --git a/flang/test/Fir/types-to-llvm.fir b/flang/test/Fir/types-to-llvm.fir
--- a/flang/test/Fir/types-to-llvm.fir
+++ b/flang/test/Fir/types-to-llvm.fir
@@ -203,3 +203,11 @@
 func private @foo16(%arg0: !fir.vector<2:!fir.real<16>>)
 // CHECK-LABEL: foo16
 // CHECK-SAME: vector<2xf128>
+
+// -----
+
+// Test `!fir.len` conversion.
+
+func private @foo0(%arg0: !fir.len)
+// CHECK-LABEL: foo0
+// CHECK-SAME: i32