diff --git a/lib/Sema/FlowChecker-expr.cpp b/lib/Sema/FlowChecker-expr.cpp
index 11ece91f1d5..6d6d72d8cfe 100644
--- a/lib/Sema/FlowChecker-expr.cpp
+++ b/lib/Sema/FlowChecker-expr.cpp
@@ -1894,10 +1894,17 @@ class FlowChecker::ExprVisitor {
       auto [argTypeNarrow, cf] = tryNarrowType(argType, expectedType);
 
       if (!cf.canFlow) {
-        outer_.sm_.error(
-            arg->getSourceRange(),
-            "ft: " + calleeName + " parameter '" + param.first.str() +
-                "' type mismatch");
+        if (param.first.isValid()) {
+          outer_.sm_.error(
+              arg->getSourceRange(),
+              "ft: " + calleeName + " parameter '" + param.first.str() +
+                  "' type mismatch");
+        } else {
+          outer_.sm_.error(
+              arg->getSourceRange(),
+              "ft: " + calleeName + " parameter #" + llvh::Twine(argIndex + 1) +
+                  " type mismatch");
+        }
         return false;
       }
       // If a cast is needed, replace the argument with the cast.
diff --git a/test/Sema/flow/regress-function-param-no-name-error.js b/test/Sema/flow/regress-function-param-no-name-error.js
new file mode 100644
index 00000000000..9b3a5770b41
--- /dev/null
+++ b/test/Sema/flow/regress-function-param-no-name-error.js
@@ -0,0 +1,19 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+// RUN: (! %shermes -Werror -ferror-limit=0 -typed -dump-sema %s 2>&1 ) | %FileCheckOrRegen --match-full-lines %s
+
+function f(cb: number => string) {
+  cb('a');
+}
+
+// Auto-generated content below. Please do not modify manually.
+
+// CHECK:{{.*}}regress-function-param-no-name-error.js:11:6: error: ft: function parameter #1 type mismatch
+// CHECK-NEXT:  cb('a');
+// CHECK-NEXT:     ^~~
+// CHECK-NEXT:Emitted 1 errors. exiting.