diff --git a/src/pthreads.c b/src/pthreads.c
--- a/src/pthreads.c
+++ b/src/pthreads.c
@@ -77,8 +77,12 @@
 #if defined(_MSC_VER)
 #include <malloc.h>
 #define alloca _alloca
 #elif !defined(alloca) && defined(__GNUC__)
 #define alloca(s) __builtin_alloca(s)
 #else
+#if defined(__FreeBSD__)
+/* alloca already defined in <stdlib.h> via __builtin_alloca on FreeBSD */
+#else
 #include <alloca.h>
+#endif
 #endif