diff --git a/src/Type.h b/src/Type.h
index a2054473d3..a28a32c45d 100644
--- a/src/Type.h
+++ b/src/Type.h
@@ -429,6 +429,8 @@ public:
 		bool deprecated;
 		std::string deprecation_msg;
 		RecordTypePtr args;
+		// Maps from parameter index in canonical prototype to
+		// parameter index in this alternate prorotype.
 		std::map<int, int> offsets;
 	};
 
diff --git a/src/Var.cc b/src/Var.cc
index 535c9ab096..16e474ea02 100644
--- a/src/Var.cc
+++ b/src/Var.cc
@@ -96,7 +96,7 @@ static bool add_prototype(const zeek::detail::IDPtr& id, zeek::Type* t,
 			return false;
 			}
 
-		offsets[i] = o;
+		offsets[o] = i;
 		}
 
 	auto deprecated = false;
@@ -604,24 +604,54 @@ void begin_func(zeek::detail::IDPtr id, const char* module_name,
 	else
 		id->SetType(t);
 
+	const auto& args = t->Params();
+	const auto& canon_args = id->GetType()->AsFuncType()->Params();
+
 	zeek::detail::push_scope(std::move(id), std::move(attrs));
 
-	const auto& args = t->Params();
-	int num_args = args->NumFields();
-
-	for ( int i = 0; i < num_args; ++i )
+	for ( int i = 0; i < canon_args->NumFields(); ++i )
 		{
-		zeek::TypeDecl* arg_i = args->FieldDecl(i);
+		zeek::TypeDecl* arg_i;
+		bool hide = false;
+
+		if ( prototype )
+			{
+			auto it = prototype->offsets.find(i);
+
+			if ( it == prototype->offsets.end() )
+				{
+				// Alternate prototype hides this param
+				hide = true;
+				arg_i = canon_args->FieldDecl(i);
+				}
+			else
+				{
+				// Alternate prototype maps this param to another index
+				arg_i = args->FieldDecl(it->second);
+				}
+			}
+		else
+			{
+			if ( i < args->NumFields() )
+				arg_i = args->FieldDecl(i);
+			else
+				break;
+			}
+
 		auto arg_id = zeek::detail::lookup_ID(arg_i->id, module_name);
 
 		if ( arg_id && ! arg_id->IsGlobal() )
 			arg_id->Error("argument name used twice");
 
-		arg_id = zeek::detail::install_ID(arg_i->id, module_name, false, false);
-		arg_id->SetType(arg_i->type);
+		const char* local_name = arg_i->id;
 
-		if ( prototype )
-			arg_id->SetOffset(prototype->offsets[i]);
+		if ( hide )
+			// Note the illegal '-' in hidden name implies we haven't
+			// clobbered any local variable names.
+			local_name = fmt("%s-hidden", local_name);
+
+		arg_id = zeek::detail::install_ID(local_name, module_name, false, false);
+		arg_id->SetType(arg_i->type);
 		}
 
 	if ( zeek::detail::Attr* depr_attr = find_attr(zeek::detail::current_scope()->Attrs().get(),
diff --git a/testing/btest/Baseline/language.alternate-prototypes-deprecated-args/hidden-error b/testing/btest/Baseline/language.alternate-prototypes-deprecated-args/hidden-error
new file mode 100644
index 0000000000..3e7b9120c4
--- /dev/null
+++ b/testing/btest/Baseline/language.alternate-prototypes-deprecated-args/hidden-error
@@ -0,0 +1,3 @@
+warning in /home/jon/pro/zeek/zeek/testing/btest/.tmp/language.alternate-prototypes-deprecated-args/alternate-prototypes-deprecated-args.zeek, line 11 and /home/jon/pro/zeek/zeek/testing/btest/.tmp/language.alternate-prototypes-deprecated-args/alternate-prototypes-deprecated-args.zeek, line 7: use of deprecated parameter 'b': Don't use 'b' (event(a:string; b:string; c:string;))
+warning in /home/jon/pro/zeek/zeek/testing/btest/.tmp/language.alternate-prototypes-deprecated-args/alternate-prototypes-deprecated-args.zeek, line 30 and /home/jon/pro/zeek/zeek/testing/btest/.tmp/language.alternate-prototypes-deprecated-args/alternate-prototypes-deprecated-args.zeek, line 9: use of deprecated 'myev' prototype: Don't use this prototype (event(a:string; b:string;))
+error in ./hide.zeek, line 5: unknown identifier b, at or near "b"
diff --git a/testing/btest/Baseline/language.alternate-prototypes-deprecated-args/out b/testing/btest/Baseline/language.alternate-prototypes-deprecated-args/out
index 8a8d8e5b88..b3686a0b23 100644
--- a/testing/btest/Baseline/language.alternate-prototypes-deprecated-args/out
+++ b/testing/btest/Baseline/language.alternate-prototypes-deprecated-args/out
@@ -1,5 +1,8 @@
-warning in /home/jon/pro/zeek/zeek/testing/btest/.tmp/language.alternate-prototypes-deprecated-args/alternate-prototypes-deprecated-args.zeek, line 9 and /home/jon/pro/zeek/zeek/testing/btest/.tmp/language.alternate-prototypes-deprecated-args/alternate-prototypes-deprecated-args.zeek, line 5: use of deprecated parameter 'b': Don't use 'b' (event(a:string; b:string; c:string;))
-warning in /home/jon/pro/zeek/zeek/testing/btest/.tmp/language.alternate-prototypes-deprecated-args/alternate-prototypes-deprecated-args.zeek, line 19 and /home/jon/pro/zeek/zeek/testing/btest/.tmp/language.alternate-prototypes-deprecated-args/alternate-prototypes-deprecated-args.zeek, line 7: use of deprecated 'myev' prototype: Don't use this prototype (event(a:string; b:string;))
+warning in /home/jon/pro/zeek/zeek/testing/btest/.tmp/language.alternate-prototypes-deprecated-args/alternate-prototypes-deprecated-args.zeek, line 11 and /home/jon/pro/zeek/zeek/testing/btest/.tmp/language.alternate-prototypes-deprecated-args/alternate-prototypes-deprecated-args.zeek, line 7: use of deprecated parameter 'b': Don't use 'b' (event(a:string; b:string; c:string;))
+warning in /home/jon/pro/zeek/zeek/testing/btest/.tmp/language.alternate-prototypes-deprecated-args/alternate-prototypes-deprecated-args.zeek, line 30 and /home/jon/pro/zeek/zeek/testing/btest/.tmp/language.alternate-prototypes-deprecated-args/alternate-prototypes-deprecated-args.zeek, line 9: use of deprecated 'myev' prototype: Don't use this prototype (event(a:string; b:string;))
 myev (canon), one, two, three
-myev (new), one, three
+myev (new), one, three, [1, 2, 3]
+myev (new), one, three, 0
+myev (new), one, three, 1
+myev (new), one, three, 2
 myev (old), one, two
diff --git a/testing/btest/language/alternate-prototypes-deprecated-args.zeek b/testing/btest/language/alternate-prototypes-deprecated-args.zeek
index 659c4c7a16..d6c40425eb 100644
--- a/testing/btest/language/alternate-prototypes-deprecated-args.zeek
+++ b/testing/btest/language/alternate-prototypes-deprecated-args.zeek
@@ -1,6 +1,8 @@
 # @TEST-EXEC: zeek -b %INPUT >out 2>&1
 #
+# @TEST-EXEC-FAIL: zeek -b %INPUT hide.zeek >hidden-error 2>&1
 # @TEST-EXEC: TEST_DIFF_CANONIFIER=$SCRIPTS/diff-remove-abspath btest-diff out
+# @TEST-EXEC: TEST_DIFF_CANONIFIER=$SCRIPTS/diff-remove-abspath btest-diff hidden-error
 
 global myev: event(a: string, b: string &deprecated="Don't use 'b'", c: string);
 global myev: event(a: string, c: string);
@@ -13,7 +15,16 @@ event myev(a: string, b: string, c: string) &priority=11
 
 event myev(a: string, c: string) &priority = 7
 	{
-	print "myev (new)", a, c;
+	local ddd = vector(1,2,3);
+	print "myev (new)", a, c, ddd;
+	}
+
+global eee = vector(1,2,3);
+
+event myev(a: string, c: string) &priority = 6
+	{
+	for ( o in eee )
+		print "myev (new)", a, c, o;
 	}
 
 event myev(a: string, b: string) &priority = 5
@@ -26,3 +37,11 @@ event zeek_init()
 	event myev("one", "two", "three");
 	}
 
+@TEST-START-FILE hide.zeek
+event myev(a: string, c: string) &priority = 7
+	{
+	local ddd = vector(1,2,3);
+	print "myev (new)", a, c, ddd;
+	print b;
+	}
+@TEST-END-FILE