diff --git a/plugins/completion/nvim-cmp/default.nix b/plugins/completion/nvim-cmp/default.nix
index 911eaf24..ab4d95aa 100644
--- a/plugins/completion/nvim-cmp/default.nix
+++ b/plugins/completion/nvim-cmp/default.nix
@@ -505,7 +505,7 @@ in {
                           && ((length modes) >= 1)
                         )
                         ("," + (helpers.toLuaObject modes));
-                    in "cmp.mapping(${mapping.action}${modesString})"
+                    in "cmp.mapping(${action.action}${modesString})"
                   )
               )
               mapping);
diff --git a/tests/test-sources/plugins/completion/nvim-cmp.nix b/tests/test-sources/plugins/completion/nvim-cmp.nix
index 4488e047..1920798f 100644
--- a/tests/test-sources/plugins/completion/nvim-cmp.nix
+++ b/tests/test-sources/plugins/completion/nvim-cmp.nix
@@ -11,6 +11,34 @@
     };
   };
 
+  # Issue #536
+  mappings = {
+    plugins.nvim-cmp = {
+      enable = true;
+      mapping = {
+        "<CR>" = "cmp.mapping.confirm({ select = false })";
+        "<Tab>" = {
+          modes = ["i" "s"];
+          action = ''
+            function(fallback)
+              if cmp.visible() then
+                cmp.select_next_item()
+              elseif luasnip.expandable() then
+                luasnip.expand()
+              elseif luasnip.expand_or_jumpable() then
+                luasnip.expand_or_jump()
+              elseif check_backspace() then
+                fallback()
+              else
+                fallback()
+              end
+            end
+          '';
+        };
+      };
+    };
+  };
+
   # All the upstream default options of nvim-cmp
   defaults = {
     plugins.nvim-cmp = {