Index: gc.c
===================================================================
--- gc.c	(revision 34318)
+++ gc.c	(working copy)
@@ -536,10 +536,19 @@
 }
 #endif
 
+#ifdef __OpenBSD__
+/* OpenBSD posix_memalign() is broken. Quoting BUGS in manual:
+ * "Only alignments up to the page size can be specified."
+ * Minimal page size is 4KB. */
+#define HEAP_ALIGN_LOG 12
+#define HEAP_ALIGN 0x1000
+#define HEAP_ALIGN_MASK 0x0fff
+#else
 /* tiny heap size: 16KB */
 #define HEAP_ALIGN_LOG 14
 #define HEAP_ALIGN 0x4000
 #define HEAP_ALIGN_MASK 0x3fff
+#endif
 #define REQUIRED_SIZE_BY_MALLOC (sizeof(size_t) * 5)
 #define HEAP_SIZE (HEAP_ALIGN - REQUIRED_SIZE_BY_MALLOC)