diff --git a/src/hb-blob.c b/src/hb-blob.c
index 6939049..178bc8e 100644
--- a/src/hb-blob.c
+++ b/src/hb-blob.c
@@ -28,8 +28,12 @@
 
 #include "hb-blob.h"
 
+#ifdef HAVE_MPROTECT
+#ifdef HAVE_UNISTD_H
 #include <unistd.h>
+#endif /* HAVE_UNISTD_H */
 #include <sys/mman.h>
+#endif /* HAVE_MPROTECT */
 
 struct _hb_blob_t {
   hb_reference_count_t ref_count;
@@ -240,6 +244,7 @@
 
   hb_mutex_lock (blob->lock);
 
+#ifdef HAVE_MPROTECT
   if (blob->mode == HB_MEMORY_MODE_READONLY_MAY_MAKE_WRITEABLE) {
     unsigned int pagesize, mask, length;
     const char *addr;
@@ -281,6 +286,9 @@
 	     addr, addr+length, length);
 #endif
   }
+#else /* !HAVE_MPROTECT */
+#warning "No way to make readonly memory writeable.  This is suboptimal."
+#endif
 
 done:
   mode = blob->mode;