diff --git a/build.zig b/build.zig
index 1e59d84658b370ad64a9b6db381ce4f137ea0155..385d4d5b7e0288d79a07c4c2c314cb7e6bc30c5d 100644
--- a/build.zig
+++ b/build.zig
@@ -720,18 +720,27 @@ pub fn build(b: *std.Build) !void {
     check_mingw_step.dependOn(&check_mingw_run.step);
 
     {
-        const gpo_step = b.step("gen-parser-oracle", "Regenerate lib/std/zig/parser_generated_oracle.zig from doc/langref/grammar.peg");
-        const gpo_exe = b.addExecutable(.{
+        const gen_oracle_exe = b.addExecutable(.{
             .name = "gen_parser_oracle",
             .root_module = b.createModule(.{
                 .root_source_file = b.path("tools/gen_parser_oracle.zig"),
                 .target = b.graph.host,
             }),
         });
-        const gpo_run = b.addRunArtifact(gpo_exe);
-        gpo_run.addFileArg(b.path("doc/langref/grammar.peg"));
-        gpo_run.addFileArg(b.path("lib/std/zig/parser_generated_oracle.zig"));
-        gpo_step.dependOn(&gpo_run.step);
+
+        const gen_oracle_step = b.step("gen-parser-oracle", "Regenerate lib/std/zig/parser_generated_oracle.zig from doc/langref/grammar.peg");
+        const gen_oracle_run = b.addRunArtifact(gen_oracle_exe);
+        gen_oracle_run.addFileArg(b.path("doc/langref/grammar.peg"));
+        gen_oracle_run.addFileArg(b.path("lib/std/zig/parser_generated_oracle.zig"));
+        gen_oracle_step.dependOn(&gen_oracle_run.step);
+
+        const check_oracle_step = b.step("check-parser-oracle", "Check if doc/langref/grammar.peg was modified without regenerating the oracle");
+        const check_oracle_run = b.addRunArtifact(gen_oracle_exe);
+        check_oracle_run.addFileArg(b.path("doc/langref/grammar.peg"));
+        check_oracle_run.addFileArg(b.path("lib/std/zig/parser_generated_oracle.zig"));
+        check_oracle_run.addArg("--check");
+        check_oracle_step.dependOn(&check_oracle_run.step);
+        test_step.dependOn(check_oracle_step);
     }
 
     const test_incremental_step = b.step("test-incremental", "Run the incremental compilation test cases");
diff --git a/tools/gen_parser_oracle.zig b/tools/gen_parser_oracle.zig
index a5bad1238ec74748d654e92b962ef7fa360da609..fafed31eb9eeea1fa0cf69fe9a75374a7bd78b6d 100644
--- a/tools/gen_parser_oracle.zig
+++ b/tools/gen_parser_oracle.zig
@@ -1,5 +1,6 @@
 //! Example usage:
 //! zig build gen-parser-oracle
+//! zig build check-parser-oracle
 
 // This program implements a subset of the PEG grammar definition
 // in the peg(1) man page.
@@ -22,6 +23,7 @@ pub fn main(init: std.process.Init) !void {
 
     const grammar_path = args[1];
     const out_path = args[2];
+    const check = args.len > 3 and mem.eql(u8, args[3], "--check");
 
     const grammar = try Io.Dir.cwd().readFileAlloc(io, grammar_path, gpa, .unlimited);
     defer gpa.free(grammar);
@@ -53,13 +55,27 @@ pub fn main(init: std.process.Init) !void {
         return error.ParseError;
     }
 
-    var out_file = try Io.Dir.cwd().createFile(io, out_path, .{});
-    var out_buffer: [4096]u8 = undefined;
-    var out_writer = out_file.writer(io, &out_buffer);
-    const out = &out_writer.interface;
+    if (check) {
+        const current = try Io.Dir.cwd().readFileAlloc(io, out_path, gpa, .unlimited);
+        defer gpa.free(current);
+        var aw: Io.Writer.Allocating = .init(gpa);
+        defer aw.deinit();
+        try tree.render(gpa, &aw.writer, .{});
+        if (!mem.eql(u8, current, aw.written())) {
+            std.log.err("grammar.peg modified without regenerating oracle", .{});
+            std.log.info("Run zig build gen-parser-oracle to regenerate", .{});
+            std.process.exit(1);
+        }
+    } else {
+        var out_file = try Io.Dir.cwd().createFile(io, out_path, .{});
+        defer out_file.close(io);
+        var out_buffer: [4096]u8 = undefined;
+        var out_writer = out_file.writer(io, &out_buffer);
+        const out = &out_writer.interface;
 
-    try tree.render(gpa, out, .{});
-    try out.flush();
+        try tree.render(gpa, out, .{});
+        try out.flush();
+    }
 }
 
 const Generator = struct {