diff --git a/tests/all-package-defaults.nix b/tests/all-package-defaults.nix
index 8ee43e32..0bb89797 100644
--- a/tests/all-package-defaults.nix
+++ b/tests/all-package-defaults.nix
@@ -53,6 +53,10 @@ let
     "swiftformat"
     "swift-format"
   ]
+  ++ lib.optionals hostPlatform.isLinux [
+    # 2026-07-12 dependency z3 has a build failure
+    "fstar"
+  ]
   ++ lib.optionals (hostPlatform.isLinux && hostPlatform.isAarch64) [
     # 2026-06-15: semgrep fails its installCheckPhase
     "semgrep"
diff --git a/tests/lsp-servers.nix b/tests/lsp-servers.nix
index 23baf8f7..19903c30 100644
--- a/tests/lsp-servers.nix
+++ b/tests/lsp-servers.nix
@@ -37,6 +37,9 @@ let
     let
 
       disabled = [
+        # 2026-07-12 dependency z3 has a build failure
+        "fstar"
+
         # 2026-07-12 dependency python3.frictionless has a build failure
         "vectorcode_server"