diff --git a/compiler/sigmatch.nim b/compiler/sigmatch.nim
index 51728b103a2c..61a4395f33c0 100644
--- a/compiler/sigmatch.nim
+++ b/compiler/sigmatch.nim
@@ -2150,6 +2150,8 @@ proc paramTypesMatchAux(m: var TCandidate, f, a: PType,
     elif arg.sym.kind in {skMacro, skTemplate}:
       return nil
     else:
+      if arg.sym.ast == nil:
+        return nil
       let inferred = c.semGenerateInstance(c, arg.sym, m.bindings, arg.info)
       result = newSymNode(inferred, arg.info)
     if r == isInferredConvertible:
diff --git a/tests/misc/t16541.nim b/tests/misc/t16541.nim
new file mode 100644
index 000000000000..452327e8fa38
--- /dev/null
+++ b/tests/misc/t16541.nim
@@ -0,0 +1,12 @@
+discard """
+  action: "reject"
+
+"""
+
+import strutils, sugar, nre
+
+proc my_replace*(s: string, r: Regex, by: string | (proc (match: string): string)): string =
+  nre.replace(s, r, by)
+
+discard my_replace("abcde", re"[bcd]", match => match.to_upper) == "aBCDe"
+discard my_replace("abcde", re"[bcd]", (match: string) => match.to_upper) == "aBCDe"