diff --git a/.github/workflows/nix.yaml b/.github/workflows/nix.yaml
index 212befa5fe..3b1211474c 100644
--- a/.github/workflows/nix.yaml
+++ b/.github/workflows/nix.yaml
@@ -134,4 +134,5 @@ jobs:
 
       - name: Test nix run
         run: |
+          nix run -L .#nativelink-prevent-store-conflict-test
           nix run -L .#nativelink-is-executable-test
diff --git a/flake.nix b/flake.nix
index 81a7baaa16..9ac3b92b87 100644
--- a/flake.nix
+++ b/flake.nix
@@ -133,6 +133,8 @@
 
         local-image-test = pkgs.callPackage ./tools/local-image-test.nix {};
 
+        nativelink-prevent-store-conflict-test = pkgs.callPackage ./tools/nativelink-prevent-store-conflict-test.nix {inherit nativelink;};
+
         nativelink-is-executable-test = pkgs.callPackage ./tools/nativelink-is-executable-test.nix {inherit nativelink;};
 
         rbe-configs-gen = pkgs.callPackage ./local-remote-execution/rbe-configs-gen.nix {};
@@ -251,7 +253,7 @@
           };
         };
         packages = rec {
-          inherit publish-ghcr local-image-test nativelink-is-executable-test nativelink nativelink-debug native-cli lre-cc nativelink-worker-init;
+          inherit publish-ghcr local-image-test nativelink-prevent-store-conflict-test nativelink-is-executable-test nativelink nativelink-debug native-cli lre-cc nativelink-worker-init;
           default = nativelink;
 
           rbe-autogen-lre-cc = rbe-autogen lre-cc;
diff --git a/src/bin/nativelink.rs b/src/bin/nativelink.rs
index 21f1b073f0..e3bf624396 100644
--- a/src/bin/nativelink.rs
+++ b/src/bin/nativelink.rs
@@ -243,6 +243,23 @@ async fn inner_main(
         // Currently we only support http as our socket type.
         let ListenerConfig::http(http_config) = server_cfg.listener;
 
+        // Check if CAS and AC use the same store.
+        if let Some(cas_config) = &services.cas {
+            if let Some(ac_config) = &services.ac {
+                for (instance_name, cas_store_config) in cas_config {
+                    if let Some(ac_store_config) = ac_config.get(instance_name) {
+                        if cas_store_config.cas_store == ac_store_config.ac_store {
+                            return Err(make_err!(
+                                Code::InvalidArgument,
+                                "CAS and AC cannot use the same store '{}' in the config",
+                                cas_store_config.cas_store
+                            ))?;
+                        }
+                    }
+                }
+            }
+        }
+
         let tonic_services = TonicServer::builder()
             .add_optional_service(
                 services
diff --git a/tools/nativelink-prevent-store-conflict-test.nix b/tools/nativelink-prevent-store-conflict-test.nix
new file mode 100644
index 0000000000..4306722678
--- /dev/null
+++ b/tools/nativelink-prevent-store-conflict-test.nix
@@ -0,0 +1,72 @@
+{
+  nativelink,
+  writeShellScriptBin,
+}:
+writeShellScriptBin "prevent-store-conflict-test" ''
+  set -xuo pipefail
+
+  cat > store_conflict_test.json <<EOF
+  {
+    "stores": {
+      "FILESYSTEM_STORE": {
+        "compression": {
+          "compression_algorithm": {
+            "lz4": {}
+          },
+          "backend": {
+            "filesystem": {
+              "content_path": "~/.cache/nativelink/content_path-cas",
+              "temp_path": "~/.cache/nativelink/tmp_path-cas",
+              "eviction_policy": {
+                // 10gb.
+                "max_bytes": 10000000000,
+              }
+            }
+          }
+        }
+      }
+    },
+    "servers": [{
+      "listener": {
+        "http": {
+          "socket_address": "0.0.0.0:50053"
+        }
+      },
+      "services": {
+        "cas": {
+          "main": {
+            "cas_store": "FILESYSTEM_STORE"
+          }
+        },
+        "ac": {
+          "main": {
+            "ac_store": "FILESYSTEM_STORE"
+          }
+        },
+        "capabilities": {},
+        "bytestream": {
+          "cas_stores": {
+            "main": "FILESYSTEM_STORE",
+          }
+        }
+      }
+    }]
+  }
+  EOF
+
+  nativelink_output="$(${nativelink}/bin/nativelink ./store_conflict_test.json 2>&1)"
+
+  rm ./store_conflict_test.json
+
+  print_error_output=$(cat <<EOF
+  Error: Error { code: InvalidArgument, messages: ["CAS and AC cannot use the same store 'FILESYSTEM_STORE' in the config"] }
+  EOF)
+
+  if [ "$nativelink_output" = "$print_error_output" ]; then
+    echo "The output of nativelink matches the print_error output."
+  else
+    echo 'The output of nativelink does not match the print_error output:'
+    diff <(echo "$nativelink_output") <(echo "$print_error_output") >&2
+    exit 1
+  fi
+''