diff --git a/src/tools/compiletest/src/runtest.rs b/src/tools/compiletest/src/runtest.rs
index ce6569f5537da..59fce44d1c725 100644
--- a/src/tools/compiletest/src/runtest.rs
+++ b/src/tools/compiletest/src/runtest.rs
@@ -3735,15 +3735,14 @@ impl<'test> TestCx<'test> {
         }
 
         if self.config.bless {
-            cmd.env("RUSTC_BLESS_TEST", "--bless");
-            // Assume this option is active if the environment variable is "defined", with _any_ value.
-            // As an example, a `Makefile` can use this option by:
+            // If we're running in `--bless` mode, set an environment variable to tell
+            // `run_make_support` to bless snapshot files instead of checking them.
             //
-            //   ifdef RUSTC_BLESS_TEST
-            //       cp "$(TMPDIR)"/actual_something.ext expected_something.ext
-            //   else
-            //       $(DIFF) expected_something.ext "$(TMPDIR)"/actual_something.ext
-            //   endif
+            // The value is this test's source directory, because the support code
+            // will need that path in order to bless the _original_ snapshot files,
+            // not the copies in `rmake_out`.
+            // (See <https://github.com/rust-lang/rust/issues/129038>.)
+            cmd.env("RUSTC_BLESS_TEST", &self.testpaths.file);
         }
 
         if self.config.target.contains("msvc") && !self.config.cc.is_empty() {
diff --git a/src/tools/run-make-support/src/diff/mod.rs b/src/tools/run-make-support/src/diff/mod.rs
index b0ed4d5445c48..ee48e3733668d 100644
--- a/src/tools/run-make-support/src/diff/mod.rs
+++ b/src/tools/run-make-support/src/diff/mod.rs
@@ -112,14 +112,8 @@ impl Diff {
         let (expected_name, actual_name, output, actual) = self.run_common();
 
         if !output.is_empty() {
-            // If we can bless (meaning we have a file to write into and the `RUSTC_BLESS_TEST`
-            // environment variable set), then we write into the file and return.
-            if let Some(ref expected_file) = self.expected_file {
-                if std::env::var("RUSTC_BLESS_TEST").is_ok() {
-                    println!("Blessing `{}`", expected_file.display());
-                    fs::write(expected_file, actual);
-                    return;
-                }
+            if self.maybe_bless_expected_file(&actual) {
+                return;
             }
             panic!(
                 "test failed: `{}` is different from `{}`\n\n{}",
@@ -134,14 +128,8 @@ impl Diff {
         let (expected_name, actual_name, output, actual) = self.run_common();
 
         if output.is_empty() {
-            // If we can bless (meaning we have a file to write into and the `RUSTC_BLESS_TEST`
-            // environment variable set), then we write into the file and return.
-            if let Some(ref expected_file) = self.expected_file {
-                if std::env::var("RUSTC_BLESS_TEST").is_ok() {
-                    println!("Blessing `{}`", expected_file.display());
-                    fs::write(expected_file, actual);
-                    return;
-                }
+            if self.maybe_bless_expected_file(&actual) {
+                return;
             }
             panic!(
                 "test failed: `{}` is not different from `{}`\n\n{}",
@@ -149,4 +137,24 @@ impl Diff {
             )
         }
     }
+
+    /// If we have an expected file to write into, and `RUSTC_BLESS_TEST` is
+    /// set, then write the actual output into the file and return `true`.
+    ///
+    /// We assume that `RUSTC_BLESS_TEST` contains the path to the original test's
+    /// source directory. That lets us bless the original snapshot file in the
+    /// source tree, not the copy in `rmake_out` that we would normally use.
+    fn maybe_bless_expected_file(&self, actual: &str) -> bool {
+        let Some(ref expected_file) = self.expected_file else {
+            return false;
+        };
+        let Ok(bless_dir) = std::env::var("RUSTC_BLESS_TEST") else {
+            return false;
+        };
+
+        let bless_file = Path::new(&bless_dir).join(expected_file);
+        println!("Blessing `{}`", bless_file.display());
+        fs::write(bless_file, actual);
+        true
+    }
 }