diff --git a/ext/zlib/gzlib.c b/ext/zlib/gzlib.c
index fae202ef89..04093e0a80 100644
--- a/ext/zlib/gzlib.c
+++ b/ext/zlib/gzlib.c
@@ -5,6 +5,10 @@
 
 #include "gzguts.h"
 
+#ifndef _WIN32
+#include <unistd.h>
+#endif
+
 #if defined(_WIN32) && !defined(__BORLANDC__)
 #  define LSEEK _lseeki64
 #else
diff --git a/ext/zlib/gzread.c b/ext/zlib/gzread.c
index d65c0b8293..808215f65e 100644
--- a/ext/zlib/gzread.c
+++ b/ext/zlib/gzread.c
@@ -5,6 +5,10 @@
 
 #include "gzguts.h"
 
+#ifndef _WIN32
+#include <unistd.h>
+#endif
+
 /* Local functions */
 local int gz_load OF((gz_statep, unsigned char *, unsigned, unsigned *));
 local int gz_avail OF((gz_statep));
diff --git a/ext/zlib/gzwrite.c b/ext/zlib/gzwrite.c
index aa767fbf63..e805c04a80 100644
--- a/ext/zlib/gzwrite.c
+++ b/ext/zlib/gzwrite.c
@@ -5,6 +5,10 @@
 
 #include "gzguts.h"
 
+#ifndef _WIN32
+#include <unistd.h>
+#endif
+
 /* Local functions */
 local int gz_init OF((gz_statep));
 local int gz_comp OF((gz_statep, int));