diff --git a/config.toml.example b/config.toml.example
index 8b11014edae..f75e220de47 100644
--- a/config.toml.example
+++ b/config.toml.example
@@ -400,6 +400,11 @@
 # override the default allocator for rustc and LLVM.
 #jemalloc = false
 
+# Run tests in various test suites with the "nll compare mode" in addition to
+# running the tests in normal mode. Largely only used on CI and during local
+# development of NLL
+#test-compare-mode = false
+
 # =============================================================================
 # Options for specific targets
 #
diff --git a/src/bootstrap/config.rs b/src/bootstrap/config.rs
index 0f249eee000..8fc2d5787cb 100644
--- a/src/bootstrap/config.rs
+++ b/src/bootstrap/config.rs
@@ -58,6 +58,7 @@ pub struct Config {
     pub ignore_git: bool,
     pub exclude: Vec<PathBuf>,
     pub rustc_error_format: Option<String>,
+    pub test_compare_mode: bool,
 
     pub run_host_only: bool,
 
@@ -326,6 +327,7 @@ struct Rust {
     verify_llvm_ir: Option<bool>,
     remap_debuginfo: Option<bool>,
     jemalloc: Option<bool>,
+    test_compare_mode: Option<bool>,
 }
 
 /// TOML representation of how each build target is configured.
@@ -540,6 +542,7 @@ impl Config {
             set(&mut config.codegen_tests, rust.codegen_tests);
             set(&mut config.rust_rpath, rust.rpath);
             set(&mut config.jemalloc, rust.jemalloc);
+            set(&mut config.test_compare_mode, rust.test_compare_mode);
             set(&mut config.backtrace, rust.backtrace);
             set(&mut config.channel, rust.channel.clone());
             set(&mut config.rust_dist_src, rust.dist_src);
diff --git a/src/bootstrap/test.rs b/src/bootstrap/test.rs
index e6c260a1426..da827356800 100644
--- a/src/bootstrap/test.rs
+++ b/src/bootstrap/test.rs
@@ -1022,7 +1022,13 @@ impl Step for Compiletest {
             cmd.arg("--bless");
         }
 
-        let compare_mode = builder.config.cmd.compare_mode().or(self.compare_mode);
+        let compare_mode = builder.config.cmd.compare_mode().or_else(|| {
+            if builder.config.test_compare_mode {
+                self.compare_mode
+            } else {
+                None
+            }
+        });
 
         if let Some(ref nodejs) = builder.config.nodejs {
             cmd.arg("--nodejs").arg(nodejs);
diff --git a/src/ci/docker/x86_64-gnu-nopt/Dockerfile b/src/ci/docker/x86_64-gnu-nopt/Dockerfile
index d2b0dd13dc2..b0780fdf32a 100644
--- a/src/ci/docker/x86_64-gnu-nopt/Dockerfile
+++ b/src/ci/docker/x86_64-gnu-nopt/Dockerfile
@@ -16,5 +16,7 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
 COPY scripts/sccache.sh /scripts/
 RUN sh /scripts/sccache.sh
 
-ENV RUST_CONFIGURE_ARGS --build=x86_64-unknown-linux-gnu --disable-optimize-tests
+ENV RUST_CONFIGURE_ARGS --build=x86_64-unknown-linux-gnu \
+  --disable-optimize-tests \
+  --set rust.test-compare-mode
 ENV RUST_CHECK_TARGET check