diff --git a/authplane-fastmcp/pyproject.toml b/authplane-fastmcp/pyproject.toml
index 18909e7..fe0e6d9 100644
--- a/authplane-fastmcp/pyproject.toml
+++ b/authplane-fastmcp/pyproject.toml
@@ -15,7 +15,10 @@ keywords = ["oauth", "jwt", "fastmcp", "adapter", "authplane"]
 requires-python = ">=3.11"
 dependencies = [
     "authplane-sdk",
-    "fastmcp>=2.0",
+    # Upper bound on 4.x is anticipatory — when fastmcp 4 ships we need to
+    # re-verify the `FastMCP` constructor + `fastmcp.server.auth.require_scopes`
+    # surface the adapter consumes.
+    "fastmcp>=3.2,<4",
     "pydantic>=2.0",
 ]