diff --git a/Modules/_testbuffer.c b/Modules/_testbuffer.c
index 221543dcdd7..344d06d0525 100644
--- a/Modules/_testbuffer.c
+++ b/Modules/_testbuffer.c
@@ -8,13 +8,13 @@
 
 
 /* struct module */
-PyObject *structmodule = NULL;
-PyObject *Struct = NULL;
-PyObject *calcsize = NULL;
+static PyObject *structmodule = NULL;
+static PyObject *Struct = NULL;
+static PyObject *calcsize = NULL;
 
 /* cache simple format string */
 static const char *simple_fmt = "B";
-PyObject *simple_format = NULL;
+static PyObject *simple_format = NULL;
 #define SIMPLE_FORMAT(fmt) (fmt == NULL || strcmp(fmt, "B") == 0)
 #define FIX_FORMAT(fmt) (fmt == NULL ? "B" : fmt)