diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2025-12-23-23-36-41.gh-issue-143123.-51gt_.rst b/Misc/NEWS.d/next/Core_and_Builtins/2025-12-23-23-36-41.gh-issue-143123.-51gt_.rst
new file mode 100644
index 00000000000000..04523bdb615bfe
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2025-12-23-23-36-41.gh-issue-143123.-51gt_.rst
@@ -0,0 +1 @@
+Protect the JIT against recursive tracing.
diff --git a/Python/optimizer.c b/Python/optimizer.c
index 0f8ddb4ba558d3..435b39405d6e5b 100644
--- a/Python/optimizer.c
+++ b/Python/optimizer.c
@@ -138,6 +138,12 @@ _PyOptimizer_Optimize(
         // return immediately without optimization.
         return 0;
     }
+    if (_tstate->jit_tracer_state.initial_state.func == NULL) {
+        // gh-143123: It is possible for another function to finalize the current
+        // tracer's state while tracing. This might happen in a
+        // Python -> C -> Python call.
+        return 0;
+    }
     assert(!interp->compiling);
     assert(_tstate->jit_tracer_state.initial_state.stack_depth >= 0);
 #ifndef Py_GIL_DISABLED