diff --git a/src/headers/tfm.h b/src/headers/tfm.h
index d36caaa..90642cd 100644
--- a/src/headers/tfm.h
+++ b/src/headers/tfm.h
@@ -252,18 +252,16 @@
    #endif
 #endif
 
-/* platforms that can use a better rand function */
-#if defined(__FreeBSD__) || defined(__OpenBSD__) || defined(__NetBSD__) || defined(__DragonFly__)
-    #define FP_USE_ALT_RAND 1
-#endif
-
 /* use arc4random on platforms that support it */
-#ifdef FP_USE_ALT_RAND
+#if defined(__FreeBSD__) || defined(__OpenBSD__) || defined(__NetBSD__) || defined(__DragonFly__)
     #define FP_GEN_RANDOM()    arc4random()
     #define FP_GEN_RANDOM_MAX  0xffffffff
-#else
-    #define FP_GEN_RANDOM()    rand()
-    #define FP_GEN_RANDOM_MAX  RAND_MAX
+#endif
+
+/* use rand() as fall-back if there's no better rand function */
+#ifndef FP_GEN_RANDOM
+   #define FP_GEN_RANDOM()    rand()
+   #define FP_GEN_RANDOM_MAX  RAND_MAX
 #endif
 
 /* some default configurations.