diff --git a/lib/std/zig/AstGen.zig b/lib/std/zig/AstGen.zig
index b2a72d23b8..5468028ae9 100644
--- a/lib/std/zig/AstGen.zig
+++ b/lib/std/zig/AstGen.zig
@@ -5001,6 +5001,10 @@ fn structDeclInner(
     );
     if (field_comptime_bits) |bits| @memset(bits.get(astgen), 0);
 
+    const old_hasher = astgen.src_hasher;
+    defer astgen.src_hasher = old_hasher;
+    astgen.src_hasher = .init(.{});
+
     // Before any field bodies comes the backing int type, if specified.
     const backing_int_type_body_len: ?u32 = if (maybe_backing_int_node.unwrap()) |backing_int_node| len: {
         if (layout != .@"packed") return astgen.failNode(
@@ -5008,6 +5012,7 @@ fn structDeclInner(
             "non-packed struct does not support backing integer type",
             .{},
         );
+        astgen.src_hasher.update(astgen.tree.getNodeSource(backing_int_node));
         const type_ref = try typeExpr(&block_scope, &namespace.base, backing_int_node);
         if (!block_scope.endsWithNoReturn()) {
             _ = try block_scope.addBreak(.break_inline, decl_inst, type_ref);
@@ -5017,10 +5022,6 @@ fn structDeclInner(
         break :len body_len;
     } else null;
 
-    const old_hasher = astgen.src_hasher;
-    defer astgen.src_hasher = old_hasher;
-    astgen.src_hasher = .init(.{});
-
     var next_field_idx: u32 = 0;
     for (container_decl.ast.members) |member_node| {
         var member = switch (try containerMember(&block_scope, &namespace.base, &wip_decls, member_node)) {
@@ -5281,8 +5282,13 @@ fn unionDeclInner(
     const field_align_body_lens = try scratch.addOptionalSlice(scan_result.any_field_aligns, scan_result.fields_len);
     const field_value_body_lens = try scratch.addOptionalSlice(scan_result.any_field_values, scan_result.fields_len);
 
+    const old_hasher = astgen.src_hasher;
+    defer astgen.src_hasher = old_hasher;
+    astgen.src_hasher = .init(.{});
+
     // Before any field bodies comes the tag/backing type, if specified.
     const arg_type_body_len: ?u32 = if (opt_arg_node.unwrap()) |arg_node| len: {
+        astgen.src_hasher.update(astgen.tree.getNodeSource(arg_node));
         const type_ref = try typeExpr(&block_scope, &namespace.base, arg_node);
         if (!block_scope.endsWithNoReturn()) {
             _ = try block_scope.addBreak(.break_inline, decl_inst, type_ref);
@@ -5292,10 +5298,6 @@ fn unionDeclInner(
         break :len body_len;
     } else null;
 
-    const old_hasher = astgen.src_hasher;
-    defer astgen.src_hasher = old_hasher;
-    astgen.src_hasher = .init(.{});
-
     var next_field_idx: u32 = 0;
     for (members) |member_node| {
         var member = switch (try containerMember(&block_scope, &namespace.base, &wip_decls, member_node)) {
@@ -5486,8 +5488,13 @@ fn containerDecl(
             const field_names = try scratch.addSlice(fields_len);
             const field_value_body_lens = try scratch.addOptionalSlice(scan_result.any_field_values, fields_len);
 
+            const old_hasher = astgen.src_hasher;
+            defer astgen.src_hasher = old_hasher;
+            astgen.src_hasher = .init(.{});
+
             // Before any field bodies comes the tag type, if specified.
             const tag_type_body_len: ?u32 = if (container_decl.ast.arg.unwrap()) |tag_type_node| len: {
+                astgen.src_hasher.update(astgen.tree.getNodeSource(tag_type_node));
                 const type_ref = try typeExpr(&block_scope, &namespace.base, tag_type_node);
                 if (!block_scope.endsWithNoReturn()) {
                     _ = try block_scope.addBreak(.break_inline, decl_inst, type_ref);
@@ -5497,10 +5504,6 @@ fn containerDecl(
                 break :len body_len;
             } else null;
 
-            const old_hasher = astgen.src_hasher;
-            defer astgen.src_hasher = old_hasher;
-            astgen.src_hasher = .init(.{});
-
             var next_field_idx: u32 = 0;
             var opt_nonexhaustive_node: Ast.Node.OptionalIndex = .none;
             for (container_decl.ast.members) |member_node| {
diff --git a/test/incremental/change_bitpack_backing_int b/test/incremental/change_bitpack_backing_int
new file mode 100644
index 0000000000..0af16aa43e
--- /dev/null
+++ b/test/incremental/change_bitpack_backing_int
@@ -0,0 +1,77 @@
+#update=initial version
+#file=main.zig
+const Foo = packed struct(u8) { a: u4, b: i4 };
+const Bar = packed union(u10) { a: u10, b: i10 };
+pub fn main() void {}
+comptime {
+    @compileLog(@typeInfo(Foo).@"struct".backing_integer.?);
+}
+comptime {
+    @compileLog(@bitSizeOf(Bar));
+}
+const std = @import("std");
+const io = std.Io.Threaded.global_single_threaded.io();
+#expect_error=main.zig:5:5: error: found compile log statement
+#expect_error=main.zig:8:5: note: also here
+#expect_compile_log=@as(type, u8)
+#expect_compile_log=@as(comptime_int, 10)
+
+#update=make backing types signed
+#file=main.zig
+const Foo = packed struct(i8) { a: u4, b: i4 };
+const Bar = packed union(i10) { a: u10, b: i10 };
+pub fn main() void {}
+comptime {
+    @compileLog(@typeInfo(Foo).@"struct".backing_integer.?);
+}
+comptime {
+    @compileLog(@bitSizeOf(Bar));
+}
+const std = @import("std");
+const io = std.Io.Threaded.global_single_threaded.io();
+#expect_error=main.zig:5:5: error: found compile log statement
+#expect_error=main.zig:8:5: note: also here
+#expect_compile_log=@as(type, i8)
+#expect_compile_log=@as(comptime_int, 10)
+
+#update=make backing types too small
+#file=main.zig
+const Foo = packed struct(i5) { a: u4, b: i4 };
+const Bar = packed union(i8) { a: u10, b: i10 };
+pub fn main() void {}
+comptime {
+    @compileLog(@typeInfo(Foo).@"struct".backing_integer.?);
+}
+comptime {
+    @compileLog(@bitSizeOf(Bar));
+}
+const std = @import("std");
+const io = std.Io.Threaded.global_single_threaded.io();
+#expect_error=main.zig:1:20: error: backing integer bit width does not match total bit width of fields
+#expect_error=main.zig:1:27: note: backing integer 'i5' has bit width '5'
+#expect_error=main.zig:1:20: note: struct fields have total bit width '8'
+#expect_error=main.zig:2:35: error: field bit width does not match backing integer
+#expect_error=main.zig:2:35: note: field type 'u10' has bit width '10'
+#expect_error=main.zig:2:26: note: backing integer 'i8' has bit width '8'
+#expect_error=main.zig:2:35: note: all fields in a packed union must have the same bit width
+
+#update=make backing types too big
+#file=main.zig
+const Foo = packed struct(u10) { a: u4, b: i4 };
+const Bar = packed union(u32) { a: u10, b: i10 };
+pub fn main() void {}
+comptime {
+    @compileLog(@typeInfo(Foo).@"struct".backing_integer.?);
+}
+comptime {
+    @compileLog(@bitSizeOf(Bar));
+}
+const std = @import("std");
+const io = std.Io.Threaded.global_single_threaded.io();
+#expect_error=main.zig:1:20: error: backing integer bit width does not match total bit width of fields
+#expect_error=main.zig:1:27: note: backing integer 'u10' has bit width '10'
+#expect_error=main.zig:1:20: note: struct fields have total bit width '8'
+#expect_error=main.zig:2:36: error: field bit width does not match backing integer
+#expect_error=main.zig:2:36: note: field type 'u10' has bit width '10'
+#expect_error=main.zig:2:26: note: backing integer 'u32' has bit width '32'
+#expect_error=main.zig:2:36: note: all fields in a packed union must have the same bit width
diff --git a/test/incremental/change_enum_tag_type b/test/incremental/change_enum_tag_type
index 3e1d184fc8..6ff8a1424d 100644
--- a/test/incremental/change_enum_tag_type
+++ b/test/incremental/change_enum_tag_type
@@ -59,3 +59,35 @@ pub fn main() !void {
 const std = @import("std");
 const io = std.Io.Threaded.global_single_threaded.io();
 #expect_stdout="a\n"
+#update=specify tag directly
+#file=main.zig
+const Foo = enum(u3) {
+    a,
+    b,
+    c,
+    d,
+    e,
+};
+pub fn main() !void {
+    @compileLog(@typeInfo(Foo).@"enum".tag_type);
+}
+const std = @import("std");
+const io = std.Io.Threaded.global_single_threaded.io();
+#expect_error=main.zig:9:5: error: found compile log statement
+#expect_compile_log=@as(type, u3)
+#update=change directly-specified tag type
+#file=main.zig
+const Foo = enum(u8) {
+    a,
+    b,
+    c,
+    d,
+    e,
+};
+pub fn main() !void {
+    @compileLog(@typeInfo(Foo).@"enum".tag_type);
+}
+const std = @import("std");
+const io = std.Io.Threaded.global_single_threaded.io();
+#expect_error=main.zig:9:5: error: found compile log statement
+#expect_compile_log=@as(type, u8)
diff --git a/test/incremental/change_union_tag_type b/test/incremental/change_union_tag_type
new file mode 100644
index 0000000000..2e6fbf3154
--- /dev/null
+++ b/test/incremental/change_union_tag_type
@@ -0,0 +1,39 @@
+#update=initial version
+#file=main.zig
+const A = enum(u8) { a };
+const B = enum(u8) { b };
+const Foo = union(A) { a: u8 };
+pub fn main(init: std.process.Init) !void {
+    const field_name = @typeInfo(Foo).@"union".fields[0].name;
+    var stdout_writer = std.Io.File.stdout().writerStreaming(init.io, &.{});
+    try stdout_writer.interface.print("{s}\n", .{field_name});
+}
+const std = @import("std");
+#expect_stdout="a\n"
+
+#update=change tag type
+#file=main.zig
+const A = enum(u8) { a };
+const B = enum(u8) { b };
+const Foo = union(B) { a: u8 };
+pub fn main(init: std.process.Init) !void {
+    const field_name = @typeInfo(Foo).@"union".fields[0].name;
+    var stdout_writer = std.Io.File.stdout().writerStreaming(init.io, &.{});
+    try stdout_writer.interface.print("{s}\n", .{field_name});
+}
+const std = @import("std");
+#expect_error=main.zig:3:24: error: no field named 'a' in enum 'main.B'
+#expect_error=main.zig:2:11: note: enum declared here
+
+#update=change field name to match new tag type
+#file=main.zig
+const A = enum(u8) { a };
+const B = enum(u8) { b };
+const Foo = union(B) { b: u8 };
+pub fn main(init: std.process.Init) !void {
+    const field_name = @typeInfo(Foo).@"union".fields[0].name;
+    var stdout_writer = std.Io.File.stdout().writerStreaming(init.io, &.{});
+    try stdout_writer.interface.print("{s}\n", .{field_name});
+}
+const std = @import("std");
+#expect_stdout="b\n"