diff --git a/src/Var.cc b/src/Var.cc
index 8b283e4a81..caa599ed6b 100644
--- a/src/Var.cc
+++ b/src/Var.cc
@@ -76,6 +76,13 @@ static bool add_prototype(ID* id, BroType* t, attr_list* attrs,
 	for ( auto i = 0; i < alt_args->NumFields(); ++i )
 		{
 		auto field = alt_args->FieldName(i);
+
+		if ( alt_args->FieldDecl(i)->attrs )
+			{
+			alt_ft->Error(fmt("alternate function prototype arguments may not have attributes: arg '%s'", field), canon_ft);
+			return false;
+			}
+
 		auto o = canon_args->FieldOffset(field);
 
 		if ( o < 0 )
diff --git a/testing/btest/Baseline/language.alternate-prototypes-default-args/errors b/testing/btest/Baseline/language.alternate-prototypes-default-args/errors
new file mode 100644
index 0000000000..ec8fac7ea0
--- /dev/null
+++ b/testing/btest/Baseline/language.alternate-prototypes-default-args/errors
@@ -0,0 +1 @@
+error in ./bad.zeek, line 2 and ./bad.zeek, line 1: alternate function prototype arguments may not have attributes: arg 'a' (event(c:string; b:string; a:string;) and event(a:string; b:string; c:string;))
diff --git a/testing/btest/Baseline/language.alternate-prototypes-default-args/out b/testing/btest/Baseline/language.alternate-prototypes-default-args/out
new file mode 100644
index 0000000000..19682ecd68
--- /dev/null
+++ b/testing/btest/Baseline/language.alternate-prototypes-default-args/out
@@ -0,0 +1,6 @@
+foo, A, B, C
+foo, A, B, C
+reverse foo, A, B, C
+foo a, A
+foo b, B
+foo c, C
diff --git a/testing/btest/language/alternate-prototypes-default-args.zeek b/testing/btest/language/alternate-prototypes-default-args.zeek
new file mode 100644
index 0000000000..a7eeafac20
--- /dev/null
+++ b/testing/btest/language/alternate-prototypes-default-args.zeek
@@ -0,0 +1,50 @@
+# @TEST-EXEC: zeek -b %INPUT >out
+# @TEST-EXEC-FAIL: zeek -b bad.zeek >errors 2>&1
+# @TEST-EXEC: btest-diff out
+# @TEST-EXEC: TEST_DIFF_CANONIFIER=$SCRIPTS/diff-remove-abspath btest-diff errors
+
+global foo: event(a: string, b: string, c: string &default="C");
+global foo: event(c: string, b: string, a: string);
+global foo: event(a: string);
+global foo: event(b: string);
+global foo: event(c: string);
+
+event foo(a: string, b: string, c: string)
+	{
+	print "foo", a, b, c;
+	}
+
+event foo(mya: string, b: string, c: string)
+	{
+	print "foo", mya, b, c;
+	}
+
+event foo(c: string, b: string, a: string)
+	{
+	print "reverse foo", a, b, c;
+	}
+
+event foo(a: string)
+	{
+	print "foo a", a;
+	}
+
+event foo(b: string)
+	{
+	print "foo b", b;
+	}
+
+event foo(c: string)
+	{
+	print "foo c", c;
+	}
+
+event zeek_init()
+	{
+	event foo("A", "B");
+	}
+
+@TEST-START-FILE bad.zeek
+global foo: event(a: string, b: string, c: string &default="C");
+global foo: event(c: string, b: string, a: string &default="A");
+@TEST-END-FILE bad.zeek