diff --git a/pkgs/by-name/fs/fstar/z3/default.nix b/pkgs/by-name/fs/fstar/z3/default.nix
index b0429deb8d0c..e4973e669ac4 100644
--- a/pkgs/by-name/fs/fstar/z3/default.nix
+++ b/pkgs/by-name/fs/fstar/z3/default.nix
@@ -8,15 +8,17 @@
 }:
 
 let
+  z3' = z3.override { useCmakeBuild = false; };
+
   # fstar has a pretty hard dependency on certain z3 patch versions.
   # https://github.com/FStarLang/FStar/issues/3689#issuecomment-2625073641
   # We need to package all the Z3 versions it prefers here.
   fstarNewZ3Version = "4.13.3";
   fstarNewZ3 =
-    if z3.version == fstarNewZ3Version then
-      z3
+    if z3'.version == fstarNewZ3Version then
+      z3'
     else
-      z3.overrideAttrs (final: rec {
+      z3'.overrideAttrs (final: rec {
         version = fstarNewZ3Version;
         src = fetchFromGitHub {
           owner = "Z3Prover";
@@ -28,10 +30,10 @@ let
 
   fstarOldZ3Version = "4.8.5";
   fstarOldZ3 =
-    if z3.version == fstarOldZ3Version then
-      z3
+    if z3'.version == fstarOldZ3Version then
+      z3'
     else
-      z3.overrideAttrs (prev: rec {
+      z3'.overrideAttrs (prev: rec {
         version = fstarOldZ3Version;
         src = fetchFromGitHub {
           owner = "Z3Prover";