diff --git a/lib/compiler_rt/clzsi2_test.zig b/lib/compiler_rt/clzsi2_test.zig
index 4fd85edca56a..a869609e243f 100644
--- a/lib/compiler_rt/clzsi2_test.zig
+++ b/lib/compiler_rt/clzsi2_test.zig
@@ -4,7 +4,7 @@ const testing = @import("std").testing;
 
 fn test__clzsi2(a: u32, expected: i32) !void {
     const nakedClzsi2 = clz.__clzsi2;
-    const actualClzsi2 = @as(*const fn (a: i32) callconv(.C) i32, @ptrCast(&nakedClzsi2));
+    const actualClzsi2 = @as(*const fn (i32) callconv(.C) i32, @ptrCast(&nakedClzsi2));
     const x: i32 = @bitCast(a);
     const result = actualClzsi2(x);
     try testing.expectEqual(expected, result);
diff --git a/lib/compiler_rt/int.zig b/lib/compiler_rt/int.zig
index c100b815a58f..131303dff3d1 100644
--- a/lib/compiler_rt/int.zig
+++ b/lib/compiler_rt/int.zig
@@ -107,7 +107,7 @@ fn test_one_aeabi_ldivmod(a: i64, b: i64, expected_q: i64, expected_r: i64) !voi
         q: i64, // r1:r0
         r: i64, // r3:r2
     };
-    const actualIdivmod = @as(*const fn (a: i64, b: i64) callconv(.AAPCS) LdivmodRes, @ptrCast(&arm.__aeabi_ldivmod));
+    const actualIdivmod = @as(*const fn (i64, i64) callconv(.AAPCS) LdivmodRes, @ptrCast(&arm.__aeabi_ldivmod));
     const arm_res = actualIdivmod(a, b);
     try testing.expectEqual(expected_q, arm_res.q);
     try testing.expectEqual(expected_r, arm_res.r);
@@ -266,7 +266,7 @@ fn test_one_aeabi_idivmod(a: i32, b: i32, expected_q: i32, expected_r: i32) !voi
         q: i32, // r0
         r: i32, // r1
     };
-    const actualIdivmod = @as(*const fn (a: i32, b: i32) callconv(.AAPCS) IdivmodRes, @ptrCast(&arm.__aeabi_idivmod));
+    const actualIdivmod = @as(*const fn (i32, i32) callconv(.AAPCS) IdivmodRes, @ptrCast(&arm.__aeabi_idivmod));
     const arm_res = actualIdivmod(a, b);
     try testing.expectEqual(expected_q, arm_res.q);
     try testing.expectEqual(expected_r, arm_res.r);
diff --git a/lib/compiler_rt/udivmoddi4_test.zig b/lib/compiler_rt/udivmoddi4_test.zig
index 3c51ed942639..204fb9305f73 100644
--- a/lib/compiler_rt/udivmoddi4_test.zig
+++ b/lib/compiler_rt/udivmoddi4_test.zig
@@ -24,7 +24,7 @@ const ARMRes = extern struct {
 };
 
 fn test__aeabi_uldivmod(a: u64, b: u64, expected_q: u64, expected_r: u64) !void {
-    const actualUldivmod = @as(*const fn (a: u64, b: u64) callconv(.AAPCS) ARMRes, @ptrCast(&__aeabi_uldivmod));
+    const actualUldivmod = @as(*const fn (u64, u64) callconv(.AAPCS) ARMRes, @ptrCast(&__aeabi_uldivmod));
     const arm_res = actualUldivmod(a, b);
     try testing.expectEqual(expected_q, arm_res.q);
     try testing.expectEqual(expected_r, arm_res.r);
diff --git a/lib/std/os.zig b/lib/std/os.zig
index cf388f76e955..e73da813b62e 100644
--- a/lib/std/os.zig
+++ b/lib/std/os.zig
@@ -5475,7 +5475,7 @@ pub fn nanosleep(seconds: u64, nanoseconds: u64) void {
 pub fn dl_iterate_phdr(
     context: anytype,
     comptime Error: type,
-    comptime callback: fn (info: *dl_phdr_info, size: usize, context: @TypeOf(context)) Error!void,
+    comptime callback: fn (info: *dl_phdr_info, size: usize, @TypeOf(context)) Error!void,
 ) Error!void {
     const Context = @TypeOf(context);
 
diff --git a/lib/std/os/uefi/tables/boot_services.zig b/lib/std/os/uefi/tables/boot_services.zig
index 8ed8c08a0104..267e5db2e83d 100644
--- a/lib/std/os/uefi/tables/boot_services.zig
+++ b/lib/std/os/uefi/tables/boot_services.zig
@@ -44,10 +44,10 @@ pub const BootServices = extern struct {
     freePool: *const fn (buffer: [*]align(8) u8) callconv(cc) Status,
 
     /// Creates an event.
-    createEvent: *const fn (type: u32, notify_tpl: usize, notify_func: ?*const fn (Event, ?*anyopaque) callconv(cc) void, notifyCtx: ?*const anyopaque, event: *Event) callconv(cc) Status,
+    createEvent: *const fn (u32, notify_tpl: usize, notify_func: ?*const fn (Event, ?*anyopaque) callconv(cc) void, notifyCtx: ?*const anyopaque, event: *Event) callconv(cc) Status,
 
     /// Sets the type of timer and the trigger time for a timer event.
-    setTimer: *const fn (event: Event, type: TimerDelay, triggerTime: u64) callconv(cc) Status,
+    setTimer: *const fn (event: Event, timerDelay: TimerDelay, triggerTime: u64) callconv(cc) Status,
 
     /// Stops execution until an event is signaled.
     waitForEvent: *const fn (event_len: usize, events: [*]const Event, index: *usize) callconv(cc) Status,
@@ -156,7 +156,7 @@ pub const BootServices = extern struct {
     setMem: *const fn (buffer: [*]u8, size: usize, value: u8) callconv(cc) void,
 
     /// Creates an event in a group.
-    createEventEx: *const fn (type: u32, notify_tpl: usize, notify_func: EfiEventNotify, notify_ctx: *const anyopaque, event_group: *align(8) const Guid, event: *Event) callconv(cc) Status,
+    createEventEx: *const fn (u32, notify_tpl: usize, notify_func: EfiEventNotify, notify_ctx: *const anyopaque, event_group: *align(8) const Guid, event: *Event) callconv(cc) Status,
 
     /// Opens a protocol with a structure as the loaded image for a UEFI application
     pub fn openProtocolSt(self: *BootServices, comptime protocol: type, handle: Handle) !*protocol {
diff --git a/lib/std/sort.zig b/lib/std/sort.zig
index f354e80df61b..2f05fbc0ba25 100644
--- a/lib/std/sort.zig
+++ b/lib/std/sort.zig
@@ -404,7 +404,7 @@ pub fn binarySearch(
     key: anytype,
     items: []const T,
     context: anytype,
-    comptime compareFn: fn (context: @TypeOf(context), key: @TypeOf(key), mid_item: T) math.Order,
+    comptime compareFn: fn (@TypeOf(context), @TypeOf(key), mid_item: T) math.Order,
 ) ?usize {
     var left: usize = 0;
     var right: usize = items.len;
@@ -538,7 +538,7 @@ pub fn min(
     comptime T: type,
     items: []const T,
     context: anytype,
-    comptime lessThan: fn (context: @TypeOf(context), lhs: T, rhs: T) bool,
+    comptime lessThan: fn (@TypeOf(context), lhs: T, rhs: T) bool,
 ) ?T {
     const i = argMin(T, items, context, lessThan) orelse return null;
     return items[i];
@@ -558,7 +558,7 @@ pub fn argMax(
     comptime T: type,
     items: []const T,
     context: anytype,
-    comptime lessThan: fn (context: @TypeOf(context), lhs: T, rhs: T) bool,
+    comptime lessThan: fn (@TypeOf(context), lhs: T, rhs: T) bool,
 ) ?usize {
     if (items.len == 0) {
         return null;
@@ -590,7 +590,7 @@ pub fn max(
     comptime T: type,
     items: []const T,
     context: anytype,
-    comptime lessThan: fn (context: @TypeOf(context), lhs: T, rhs: T) bool,
+    comptime lessThan: fn (@TypeOf(context), lhs: T, rhs: T) bool,
 ) ?T {
     const i = argMax(T, items, context, lessThan) orelse return null;
     return items[i];
@@ -610,7 +610,7 @@ pub fn isSorted(
     comptime T: type,
     items: []const T,
     context: anytype,
-    comptime lessThan: fn (context: @TypeOf(context), lhs: T, rhs: T) bool,
+    comptime lessThan: fn (@TypeOf(context), lhs: T, rhs: T) bool,
 ) bool {
     var i: usize = 1;
     while (i < items.len) : (i += 1) {
diff --git a/lib/std/sort/pdq.zig b/lib/std/sort/pdq.zig
index d74c7788a4c1..49173529745d 100644
--- a/lib/std/sort/pdq.zig
+++ b/lib/std/sort/pdq.zig
@@ -12,7 +12,7 @@ pub fn pdq(
     comptime T: type,
     items: []T,
     context: anytype,
-    comptime lessThanFn: fn (context: @TypeOf(context), lhs: T, rhs: T) bool,
+    comptime lessThanFn: fn (@TypeOf(context), lhs: T, rhs: T) bool,
 ) void {
     const Context = struct {
         items: []T,
diff --git a/lib/std/zig/Parse.zig b/lib/std/zig/Parse.zig
index cc4f29622953..79f0c5590406 100644
--- a/lib/std/zig/Parse.zig
+++ b/lib/std/zig/Parse.zig
@@ -3996,7 +3996,7 @@ fn parseBuiltinCall(p: *Parse) !Node.Index {
 }
 
 /// IfPrefix <- KEYWORD_if LPAREN Expr RPAREN PtrPayload?
-fn parseIf(p: *Parse, comptime bodyParseFn: fn (p: *Parse) Error!Node.Index) !Node.Index {
+fn parseIf(p: *Parse, comptime bodyParseFn: fn (*Parse) Error!Node.Index) !Node.Index {
     const if_token = p.eatToken(.keyword_if) orelse return null_node;
     _ = try p.expectToken(.l_paren);
     const condition = try p.expectExpr();
diff --git a/src/AstGen.zig b/src/AstGen.zig
index 0d1fa6c06194..81b2fd98e2bd 100644
--- a/src/AstGen.zig
+++ b/src/AstGen.zig
@@ -1280,6 +1280,7 @@ fn fnProtoExpr(
     const block_inst = try gz.makeBlockInst(.block_inline, node);
 
     var noalias_bits: u32 = 0;
+    var params_scope = &block_scope.base;
     const is_var_args = is_var_args: {
         var param_type_i: usize = 0;
         var it = fn_proto.iterate(tree);
@@ -1303,26 +1304,29 @@ fn fnProtoExpr(
             } else false;
 
             const param_name: u32 = if (param.name_token) |name_token| blk: {
-                if (mem.eql(u8, "_", tree.tokenSlice(name_token)))
+                const name_bytes = tree.tokenSlice(name_token);
+                if (mem.eql(u8, "_", name_bytes))
                     break :blk 0;
 
-                break :blk try astgen.identAsString(name_token);
+                const param_name = try astgen.identAsString(name_token);
+                try astgen.detectLocalShadowing(params_scope, param_name, name_token, name_bytes, .@"function prototype parameter");
+                break :blk param_name;
             } else 0;
 
-            if (is_anytype) {
+            const param_inst = if (is_anytype) param: {
                 const name_token = param.name_token orelse param.anytype_ellipsis3.?;
 
                 const tag: Zir.Inst.Tag = if (is_comptime)
                     .param_anytype_comptime
                 else
                     .param_anytype;
-                _ = try block_scope.addStrTok(tag, param_name, name_token);
-            } else {
+                break :param try block_scope.addStrTok(tag, param_name, name_token);
+            } else param: {
                 const param_type_node = param.type_expr;
                 assert(param_type_node != 0);
                 var param_gz = block_scope.makeSubBlock(scope);
                 defer param_gz.unstack();
-                const param_type = try expr(&param_gz, scope, coerced_type_ri, param_type_node);
+                const param_type = try expr(&param_gz, params_scope, coerced_type_ri, param_type_node);
                 const param_inst_expected: Zir.Inst.Index = @enumFromInt(astgen.instructions.len + 1);
                 _ = try param_gz.addBreakWithSrcNode(.break_inline, param_inst_expected, param_type, param_type_node);
                 const main_tokens = tree.nodes.items(.main_token);
@@ -1330,53 +1334,99 @@ fn fnProtoExpr(
                 const tag: Zir.Inst.Tag = if (is_comptime) .param_comptime else .param;
                 const param_inst = try block_scope.addParam(&param_gz, tag, name_token, param_name, param.first_doc_comment);
                 assert(param_inst_expected == param_inst);
-            }
+                break :param param_inst.toRef();
+            };
+
+            if (param_name == 0) continue;
+
+            const sub_scope = try astgen.arena.create(Scope.LocalVal);
+            sub_scope.* = .{
+                .parent = params_scope,
+                .gen_zir = &block_scope,
+                .name = param_name,
+                .inst = param_inst,
+                .token_src = param.name_token.?,
+                .id_cat = .@"function prototype parameter",
+            };
+            params_scope = &sub_scope.base;
         }
         break :is_var_args false;
     };
 
+    var align_gz = block_scope.makeSubBlock(params_scope);
+    defer align_gz.unstack();
     const align_ref: Zir.Inst.Ref = if (fn_proto.ast.align_expr == 0) .none else inst: {
-        break :inst try expr(&block_scope, scope, align_ri, fn_proto.ast.align_expr);
+        const inst = try expr(&block_scope, params_scope, coerced_align_ri, fn_proto.ast.align_expr);
+        if (align_gz.instructionsSlice().len == 0) {
+            // In this case we will send a len=0 body which can be encoded more efficiently.
+            break :inst inst;
+        }
+        const param_index: Zir.Inst.Index = @enumFromInt(astgen.instructions.len + 1);
+        _ = try align_gz.addBreakWithSrcNode(.break_inline, param_index, inst, fn_proto.ast.align_expr);
+        break :inst inst;
     };
 
     if (fn_proto.ast.addrspace_expr != 0) {
         return astgen.failNode(fn_proto.ast.addrspace_expr, "addrspace not allowed on function prototypes", .{});
     }
+    var addrspace_gz = block_scope.makeSubBlock(params_scope);
+    defer addrspace_gz.unstack();
 
     if (fn_proto.ast.section_expr != 0) {
         return astgen.failNode(fn_proto.ast.section_expr, "linksection not allowed on function prototypes", .{});
     }
+    var section_gz = block_scope.makeSubBlock(params_scope);
+    defer section_gz.unstack();
 
-    const cc: Zir.Inst.Ref = if (fn_proto.ast.callconv_expr != 0)
-        try expr(
+    var cc_gz = block_scope.makeSubBlock(params_scope);
+    defer cc_gz.unstack();
+    const cc: Zir.Inst.Ref = if (fn_proto.ast.callconv_expr == 0) .none else inst: {
+        const inst = try expr(
             &block_scope,
-            scope,
-            .{ .rl = .{ .ty = .calling_convention_type } },
+            params_scope,
+            .{ .rl = .{ .coerced_ty = .calling_convention_type } },
             fn_proto.ast.callconv_expr,
-        )
-    else
-        Zir.Inst.Ref.none;
+        );
+        if (cc_gz.instructionsSlice().len == 0) {
+            // In this case we will send a len=0 body which can be encoded more efficiently.
+            break :inst inst;
+        }
+        const param_index: Zir.Inst.Index = @enumFromInt(astgen.instructions.len + 1);
+        _ = try cc_gz.addBreakWithSrcNode(.break_inline, param_index, inst, fn_proto.ast.callconv_expr);
+        break :inst inst;
+    };
 
     const maybe_bang = tree.firstToken(fn_proto.ast.return_type) - 1;
     const is_inferred_error = token_tags[maybe_bang] == .bang;
     if (is_inferred_error) {
         return astgen.failTok(maybe_bang, "function prototype may not have inferred error set", .{});
     }
-    const ret_ty = try expr(&block_scope, scope, coerced_type_ri, fn_proto.ast.return_type);
+    var ret_gz = block_scope.makeSubBlock(params_scope);
+    defer ret_gz.unstack();
+    const ret_ty = inst: {
+        const inst = try expr(&block_scope, params_scope, coerced_type_ri, fn_proto.ast.return_type);
+        if (ret_gz.instructionsSlice().len == 0) {
+            // In this case we will send a len=0 body which can be encoded more efficiently.
+            break :inst inst;
+        }
+        const param_index: Zir.Inst.Index = @enumFromInt(astgen.instructions.len + 1);
+        _ = try ret_gz.addBreakWithSrcNode(.break_inline, param_index, inst, fn_proto.ast.return_type);
+        break :inst inst;
+    };
 
     const result = try block_scope.addFunc(.{
         .src_node = fn_proto.ast.proto_node,
 
         .cc_ref = cc,
-        .cc_gz = null,
+        .cc_gz = &cc_gz,
         .align_ref = align_ref,
-        .align_gz = null,
+        .align_gz = &align_gz,
         .ret_ref = ret_ty,
-        .ret_gz = null,
+        .ret_gz = &ret_gz,
         .section_ref = .none,
-        .section_gz = null,
+        .section_gz = &section_gz,
         .addrspace_ref = .none,
-        .addrspace_gz = null,
+        .addrspace_gz = &addrspace_gz,
 
         .param_block = block_inst,
         .body_gz = null,
@@ -10926,6 +10976,7 @@ const Scope = struct {
     /// The category of identifier. These tag names are user-visible in compile errors.
     const IdCat = enum {
         @"function parameter",
+        @"function prototype parameter",
         @"local constant",
         @"local variable",
         @"switch tag capture",
diff --git a/test/cases/compile_errors/nested_generic_function_param_type_mismatch.zig b/test/cases/compile_errors/nested_generic_function_param_type_mismatch.zig
index 99f4b7a19305..fe71c52b1627 100644
--- a/test/cases/compile_errors/nested_generic_function_param_type_mismatch.zig
+++ b/test/cases/compile_errors/nested_generic_function_param_type_mismatch.zig
@@ -2,7 +2,7 @@ pub fn sort(
     comptime T: type,
     items: []T,
     context: anytype,
-    lessThan: *const fn (context: @TypeOf(context), lhs: T, rhs: T) u32,
+    lessThan: *const fn (@TypeOf(context), lhs: T, rhs: T) u32,
 ) void {
     _ = items;
     _ = lessThan;
diff --git a/test/cases/compile_errors/parameter_shadowing_global.zig b/test/cases/compile_errors/parameter_shadowing_global.zig
index 5cc837f05e7f..6ead54b9a209 100644
--- a/test/cases/compile_errors/parameter_shadowing_global.zig
+++ b/test/cases/compile_errors/parameter_shadowing_global.zig
@@ -1,12 +1,25 @@
 const Foo = struct {};
 fn f(Foo: i32) void {}
-export fn entry() void {
+export fn entry0() void {
     f(1234);
 }
 
+export fn entry1() void {
+    const foo = 0;
+    _ = fn(foo: u32) void;
+}
+
+export fn entry2() void {
+    _ = fn(arg: u8, arg: u32) void;
+}
+
 // error
 // backend=stage2
 // target=native
 //
 // :2:6: error: function parameter shadows declaration of 'Foo'
 // :1:1: note: declared here
+// :9:12: error: function prototype parameter 'foo' shadows local constant from outer scope
+// :8:11: note: previous declaration here
+// :13:21: error: redeclaration of function prototype parameter 'arg'
+// :13:12: note: previous declaration here