diff --git a/src/platform.h b/src/platform.h
index f1d8155..877e320 100644
--- a/src/platform.h
+++ b/src/platform.h
@@ -26,6 +26,12 @@
 extern "C" {
 #endif /* __cplusplus */
 
+#ifdef _WIN32
+#define DC_PRINTF_SIZE "%Iu"
+#else
+#define DC_PRINTF_SIZE "%zu"
+#endif
+
 #ifdef _MSC_VER
 #define snprintf _snprintf
 #define strcasecmp _stricmp
diff --git a/src/suunto_eonsteel.c b/src/suunto_eonsteel.c
index 09f21a9..07cd85c 100644
--- a/src/suunto_eonsteel.c
+++ b/src/suunto_eonsteel.c
@@ -137,7 +137,7 @@ static int receive_packet(suunto_eonsteel_device_t *eon, unsigned char *buffer,
 		return -1;
 	}
 	if (transferred != PACKET_SIZE) {
-		ERROR(eon->base.context, "incomplete read interrupt transfer (got %zu, expected %d)", transferred, PACKET_SIZE);
+		ERROR(eon->base.context, "incomplete read interrupt transfer (got " DC_PRINTF_SIZE ", expected %d)", transferred, PACKET_SIZE);
 		return -1;
 	}
 	if (buf[0] != 0x3f) {
diff --git a/src/uwatec_g2.c b/src/uwatec_g2.c
index 6e35104..f6b0b02 100644
--- a/src/uwatec_g2.c
+++ b/src/uwatec_g2.c
@@ -28,6 +28,7 @@
 #include "device-private.h"
 #include "usbhid.h"
 #include "array.h"
+#include "platform.h"
 
 #define ISINSTANCE(device) dc_device_isinstance((device), &uwatec_g2_device_vtable)
 
@@ -76,7 +77,7 @@ receive_data (uwatec_g2_device_t *device, dc_event_progress_t *progress, unsigne
 			return rc;
 		}
 		if (transferred != PACKET_SIZE) {
-			ERROR (device->base.context, "incomplete read interrupt transfer (got %zu, expected %d)", transferred, PACKET_SIZE);
+			ERROR (device->base.context, "incomplete read interrupt transfer (got " DC_PRINTF_SIZE  ", expected %d)", transferred, PACKET_SIZE);
 			return DC_STATUS_PROTOCOL;
 		}
 		len = buf[0];