diff --git a/Modules/_ssl.c b/Modules/_ssl.c
--- a/Modules/_ssl.c
+++ b/Modules/_ssl.c
@@ -1713,6 +1713,9 @@
         return NULL;
     }
     self->ctx = ctx;
+#ifdef OPENSSL_NPN_NEGOTIATED
+    self->npn_protocols = NULL;
+#endif
     /* Defaults */
     SSL_CTX_set_verify(self->ctx, SSL_VERIFY_NONE, NULL);
     SSL_CTX_set_options(self->ctx,
@@ -1812,6 +1815,10 @@
     if (!PyArg_ParseTuple(args, "y*:set_npn_protocols", &protos))
         return NULL;
 
+    if (self->npn_protocols != NULL) {
+        PyMem_Free(self->npn_protocols);
+    }
+
     self->npn_protocols = PyMem_Malloc(protos.len);
     if (self->npn_protocols == NULL) {
         PyBuffer_Release(&protos);