diff --git a/src/fastmcp/server/server.py b/src/fastmcp/server/server.py
index 967ef1ceb..1950d7a3b 100644
--- a/src/fastmcp/server/server.py
+++ b/src/fastmcp/server/server.py
@@ -2047,6 +2047,9 @@ class FastMCP(
 
         from fastmcp.server.providers.fastmcp_provider import FastMCPProvider
 
+        if server is self:
+            raise ValueError("Cannot mount a server onto itself")
+
         # Handle deprecated prefix parameter
         if prefix is not None:
             warnings.warn(
diff --git a/tests/server/test_server_safety.py b/tests/server/test_server_safety.py
new file mode 100644
index 000000000..2d85b098a
--- /dev/null
+++ b/tests/server/test_server_safety.py
@@ -0,0 +1,10 @@
+import pytest
+
+from fastmcp import FastMCP
+
+
+class TestMountSafety:
+    def test_self_mount_raises(self):
+        mcp = FastMCP("test")
+        with pytest.raises(ValueError, match="Cannot mount a server onto itself"):
+            mcp.mount(mcp)