diff --git a/lib/stack b/lib/stack
index f09ddce..bada26f 100644
--- a/lib/stack
+++ b/lib/stack
@@ -33,5 +33,8 @@
         if [[ ${USE_VENV} = True && -n ${PROJECT_VENV[$service]:-} ]]; then
             unset PIP_VIRTUAL_ENV
         fi
+    else
+        echo "No function declared with name 'install_${service}'."
+        exit 1
     fi
 }