diff --git a/nixpkgs_review/nix.py b/nixpkgs_review/nix.py
index f4cca19..002f6f0 100644
--- a/nixpkgs_review/nix.py
+++ b/nixpkgs_review/nix.py
@@ -56,7 +56,7 @@ def nix_shell(
     run: str | None = None,
     sandbox: bool = False,
 ) -> None:
-    nix_shell = f"{shutil.which(build_graph)}-shell"
+    nix_shell = shutil.which(build_graph + "-shell")
     if not nix_shell:
         raise RuntimeError(f"{build_graph} not found in PATH")
 
diff --git a/nixpkgs_review/utils.py b/nixpkgs_review/utils.py
index 3245f4c..42acd9a 100644
--- a/nixpkgs_review/utils.py
+++ b/nixpkgs_review/utils.py
@@ -67,8 +67,8 @@ def current_system() -> str:
 
 
 def nix_nom_tool() -> str:
-    "Return `nom` if found in $PATH"
-    if shutil.which("nom"):
+    "Return `nom` and `nom-shell` if found in $PATH"
+    if shutil.which("nom") and shutil.which("nom-shell"):
         return "nom"
 
     return "nix"