diff --git a/include/gtkwave/fstapi.c b/include/gtkwave/fstapi.c
index b19e0bcaa..5e9529d44 100644
--- a/include/gtkwave/fstapi.c
+++ b/include/gtkwave/fstapi.c
@@ -140,7 +140,7 @@ void **JenkinsIns(void *base_i, const unsigned char *mem, uint32_t length, uint3
 #include <sys/sysctl.h>
 #endif
 
-#if defined(FST_MACOSX) || defined(__MINGW32__) || defined(__OpenBSD__) || defined(__FreeBSD__)
+#if defined(FST_MACOSX) || defined(__MINGW32__) || defined(__OpenBSD__) || defined(__FreeBSD__) || defined(__NetBSD__)
 #define FST_UNBUFFERED_IO
 #endif