diff --git a/requirements.txt b/requirements.txt
index 431949b..05ca8ed 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,5 +1,11 @@
 # MCP server
-mcp[fastmcp]>=1.0.0
+# Pinned below 2.0: mcp 2.0.0 removed `mcp.server.fastmcp`, which this
+# server imports. The unpinned floor pulled 2.0.0 into a rebuild on
+# 2026-08-11 and crash-looped zerto-docs with
+# "ModuleNotFoundError: No module named 'mcp.server.fastmcp'".
+# 2.0 also drops the [fastmcp] extra. Migrating to the 2.x API is a
+# deliberate piece of work — do not lift this pin without it.
+mcp[fastmcp]>=1.0.0,<2
 pydantic>=2.0
 httpx>=0.27