diff --git a/dist/index.js b/dist/index.js
index cc1443fb..83eba6bf 100644
--- a/dist/index.js
+++ b/dist/index.js
@@ -157087,6 +157087,7 @@ async function composeOpamCacheKeys() {
     const ocamlCompiler = await RESOLVED_COMPILER;
     const repositoryUrls = OPAM_REPOSITORIES.map(([_, value]) => value).join(",");
     const osInfo = await lib.osInfo();
+    const msys2 = WINDOWS_ENVIRONMENT === "msys2" ? "msys2" : undefined;
     const plainKey = [
         PLATFORM,
         osInfo.release,
@@ -157095,7 +157096,9 @@ async function composeOpamCacheKeys() {
         ocamlCompiler,
         repositoryUrls,
         sandbox,
-    ].join(",");
+    ]
+        .concat(msys2 ?? [])
+        .join(",");
     const hash = external_node_crypto_.createHash("sha256").update(plainKey).digest("hex");
     const key = `${CACHE_PREFIX}-setup-ocaml-opam-${hash}`;
     const restoreKeys = [key];
diff --git a/dist/post/index.js b/dist/post/index.js
index b76aab7a..a69f622e 100644
--- a/dist/post/index.js
+++ b/dist/post/index.js
@@ -103712,6 +103712,7 @@ async function composeOpamCacheKeys() {
     const ocamlCompiler = await RESOLVED_COMPILER;
     const repositoryUrls = OPAM_REPOSITORIES.map(([_, value]) => value).join(",");
     const osInfo = await system.osInfo();
+    const msys2 = WINDOWS_ENVIRONMENT === "msys2" ? "msys2" : undefined;
     const plainKey = [
         PLATFORM,
         osInfo.release,
@@ -103720,7 +103721,9 @@ async function composeOpamCacheKeys() {
         ocamlCompiler,
         repositoryUrls,
         sandbox,
-    ].join(",");
+    ]
+        .concat(msys2 ?? [])
+        .join(",");
     const hash = crypto.createHash("sha256").update(plainKey).digest("hex");
     const key = `${CACHE_PREFIX}-setup-ocaml-opam-${hash}`;
     const restoreKeys = [key];
diff --git a/packages/setup-ocaml/src/cache.ts b/packages/setup-ocaml/src/cache.ts
index a778db59..7baf1402 100644
--- a/packages/setup-ocaml/src/cache.ts
+++ b/packages/setup-ocaml/src/cache.ts
@@ -50,6 +50,7 @@ async function composeOpamCacheKeys() {
   const ocamlCompiler = await RESOLVED_COMPILER;
   const repositoryUrls = OPAM_REPOSITORIES.map(([_, value]) => value).join(",");
   const osInfo = await system.osInfo();
+  const msys2 = WINDOWS_ENVIRONMENT === "msys2" ? "msys2" : undefined;
   const plainKey = [
     PLATFORM,
     osInfo.release,
@@ -58,7 +59,9 @@ async function composeOpamCacheKeys() {
     ocamlCompiler,
     repositoryUrls,
     sandbox,
-  ].join(",");
+  ]
+    .concat(msys2 ?? [])
+    .join(",");
   const hash = crypto.createHash("sha256").update(plainKey).digest("hex");
   const key = `${CACHE_PREFIX}-setup-ocaml-opam-${hash}`;
   const restoreKeys = [key];