diff --git a/Changes.md b/Changes.md
index d1e232d2a9..4e37b3cc5c 100644
--- a/Changes.md
+++ b/Changes.md
@@ -21,6 +21,8 @@ Unreleased
   [`NonEscapeCharacter`](https://tc39.es/ecma262/#prod-NonEscapeCharacter)
   correctly in JS strings (those written using `{js|string here|js}`)
   ([#469](https://github.com/melange-re/melange/pull/469))
+- [melange]: define `MELANGE` conditional compilation variable
+  ([#472](https://github.com/melange-re/melange/pull/472))
 
 0.3.2 2022-11-19
 ---------------
diff --git a/flake.lock b/flake.lock
index ca0a9b54a1..58d0cf09d6 100644
--- a/flake.lock
+++ b/flake.lock
@@ -91,11 +91,11 @@
         "pre-commit-hooks": "pre-commit-hooks"
       },
       "locked": {
-        "lastModified": 1672661134,
-        "narHash": "sha256-WqBUyKeiv+jI11ug+qP0OnZ4nngK6eBRVTGHgdzEGvc=",
+        "lastModified": 1673444666,
+        "narHash": "sha256-5YE8MyYSRRT1bA78ZCSZCCawch3/nV+WWEddkkN8cbY=",
         "owner": "nix-community",
         "repo": "dream2nix",
-        "rev": "9f6911c78dcb0832f7fcc955e847db1a5a9ce29a",
+        "rev": "898440d4f576b89018aeeb6b0d8c3dd6baa79917",
         "type": "github"
       },
       "original": {
diff --git a/jscomp/core/bs_conditional_initial.ml b/jscomp/core/bs_conditional_initial.ml
index 3c5600f50a..7dab48afe0 100644
--- a/jscomp/core/bs_conditional_initial.ml
+++ b/jscomp/core/bs_conditional_initial.ml
@@ -66,6 +66,7 @@ let setup_env () =
     Printexc.record_backtrace true;
 #endif
 
+  Rescript_cpp.replace_directive_bool "MELANGE" true;
   Rescript_cpp.replace_directive_bool "BS" true;
   Rescript_cpp.replace_directive_bool "JS" true;
   Rescript_cpp.replace_directive_string "BS_VERSION"  Melange_version.version
diff --git a/test/melange-conditional.t b/test/melange-conditional.t
new file mode 100644
index 0000000000..3749abe330
--- /dev/null
+++ b/test/melange-conditional.t
@@ -0,0 +1,21 @@
+Demonstrate the `#if MELANGE` conditional variable
+
+  $ export MELANGELIB="$INSIDE_DUNE/lib/melange"
+  $ cat > x.ml <<EOF
+  > let () =
+  > #if MELANGE then
+  >   Js.log("It's Melange");
+  > #else
+  >   Js.log2("Not Melange, type error, not 2 arguments");
+  > #end
+  > EOF
+
+  $ melc x.ml
+  // Generated by Melange
+  'use strict';
+  
+  
+  console.log("It's Melange");
+  
+  /*  Not a pure module */
+