diff --git a/src/types/capsule.rs b/src/types/capsule.rs
index 12d2232c56c..5637f8b4919 100644
--- a/src/types/capsule.rs
+++ b/src/types/capsule.rs
@@ -385,7 +385,9 @@ impl PyCapsule {
     ///
     /// # Safety
     ///
-    /// It must be known that the capsule imported by `name` contains an item of type `T`.
+    /// - It must be known that the capsule imported by `name` contains an item of type `T`.
+    /// - The contents of the capsule must not be mutated by any third-party code while the reference is alive.
+    ///   The python interpreter does _NOT_ provide any synchronization guarantees for capsules.
     pub unsafe fn import<'py, T>(py: Python<'py>, name: &CStr) -> PyResult<&'py T> {
         // SAFETY: `name` is a valid C string, thread is attached to the Python interpreter
         let ptr = unsafe { ffi::PyCapsule_Import(name.as_ptr(), false as c_int) };