diff --git a/src/tools/compiletest/src/common.rs b/src/tools/compiletest/src/common.rs
index ff059940f7cc..5e50e227dede 100644
--- a/src/tools/compiletest/src/common.rs
+++ b/src/tools/compiletest/src/common.rs
@@ -387,6 +387,8 @@ pub struct Config {
     /// True if the profiler runtime is enabled for this target.
     /// Used by the "needs-profiler-runtime" directive in test files.
     pub profiler_runtime: bool,
+
+    pub diff_command: Option<String>,
 }
 
 impl Config {
diff --git a/src/tools/compiletest/src/lib.rs b/src/tools/compiletest/src/lib.rs
index 7d6ede9bcdac..5046eea63e25 100644
--- a/src/tools/compiletest/src/lib.rs
+++ b/src/tools/compiletest/src/lib.rs
@@ -364,6 +364,7 @@ pub fn parse_config(args: Vec<String>) -> Config {
         git_merge_commit_email: matches.opt_str("git-merge-commit-email").unwrap(),
 
         profiler_runtime: matches.opt_present("profiler-runtime"),
+        diff_command: env::var("COMPILETEST_DIFF_TOOL").ok(),
     }
 }