diff --git a/lib/compress/zstd_compress.c b/lib/compress/zstd_compress.c
index 147a26644..c6d72f584 100644
--- a/lib/compress/zstd_compress.c
+++ b/lib/compress/zstd_compress.c
@@ -413,7 +413,7 @@ size_t ZSTD_CCtxParam_setParameter(
         return CCtxParams->forceWindow;
 
     case ZSTD_p_forceAttachDict : {
-        ZSTD_dictAttachPref_e pref = (ZSTD_dictAttachPref_e)value;
+        const ZSTD_dictAttachPref_e pref = (ZSTD_dictAttachPref_e)value;
         CLAMPCHECK(pref, ZSTD_dictDefaultAttach, ZSTD_dictForceCopy);
         CCtxParams->attachDictPref = pref;
         return CCtxParams->attachDictPref;