diff --git a/zconf.h b/zconf.h
index ea3b6d6..97d2fcd 100644
--- a/zconf.h
+++ b/zconf.h
@@ -506,7 +506,7 @@ typedef uLong FAR uLongf;
 #endif
 
 #ifndef z_off_t
-#  define z_off_t long
+#  define z_off_t long long
 #endif
 
 #if !defined(_WIN32) && defined(Z_LARGE64)
diff --git a/zconf.h.cmakein b/zconf.h.cmakein
index 0eced14..2e794b9 100644
--- a/zconf.h.cmakein
+++ b/zconf.h.cmakein
@@ -508,7 +508,7 @@ typedef uLong FAR uLongf;
 #endif
 
 #ifndef z_off_t
-#  define z_off_t long
+#  define z_off_t long long
 #endif
 
 #if !defined(_WIN32) && defined(Z_LARGE64)
diff --git a/zconf.h.in b/zconf.h.in
index ea3b6d6..97d2fcd 100644
--- a/zconf.h.in
+++ b/zconf.h.in
@@ -506,7 +506,7 @@ typedef uLong FAR uLongf;
 #endif
 
 #ifndef z_off_t
-#  define z_off_t long
+#  define z_off_t long long
 #endif
 
 #if !defined(_WIN32) && defined(Z_LARGE64)