diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index 4e50f1b..8ae5d2f 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -274,6 +274,16 @@
 
 #endif /* UNION_WAIT */
 
+/* Don't use the "_r" form if we don't need it (also, won't have a
+   prototype for it, at least on Solaris -- maybe others as well?). */
+#if defined(HAVE_CTERMID_R) && defined(WITH_THREAD)
+#define USE_CTERMID_R
+#endif
+
+#if defined(HAVE_TMPNAM_R) && defined(WITH_THREAD)
+#define USE_TMPNAM_R
+#endif
+
 /* Return a dictionary corresponding to the POSIX environment table */
 
 #if !defined(_MSC_VER) && ( !defined(__WATCOMC__) || defined(__QNX__) )
@@ -649,7 +659,7 @@
 	if (!PyArg_ParseTuple(args, ":ctermid"))
 		return NULL;
 
-#if defined(HAVE_CTERMID_R) && defined(WITH_THREAD)
+#ifdef USE_CTERMID_R
 	ret = ctermid_r(buffer);
 #else
         ret = ctermid(buffer);
@@ -3342,7 +3352,7 @@
 
     if (!PyArg_ParseTuple(args, ":tmpnam"))
         return NULL;
-#if defined(HAVE_TMPNAM_R) && defined(WITH_THREAD)
+#ifdef USE_TMPNAM_R
     name = tmpnam_r(buffer);
 #else
     name = tmpnam(buffer);
@@ -3350,7 +3360,7 @@
     if (name == NULL) {
         PyErr_SetObject(PyExc_OSError,
                         Py_BuildValue("is", 0,
-#ifdef HAVE_TMPNAM_R
+#ifdef USE_TMPNAM_R
                                       "unexpected NULL from tmpnam_r"
 #else
                                       "unexpected NULL from tmpnam"