diff --git a/include/rtl-sdr.h b/include/rtl-sdr.h
index 83c45ec..f79a59c 100644
--- a/include/rtl-sdr.h
+++ b/include/rtl-sdr.h
@@ -62,7 +62,7 @@ RTLSDR_API int rtlsdr_reset_buffer(rtlsdr_dev_t *dev);
 
 RTLSDR_API int rtlsdr_read_sync(rtlsdr_dev_t *dev, void *buf, int len, int *n_read);
 
-typedef void(*rtlsdr_async_read_cb_t)(const char *buf, uint32_t len, void *ctx);
+typedef void(*rtlsdr_async_read_cb_t)(unsigned char *buf, uint32_t len, void *ctx);
 
 RTLSDR_API int rtlsdr_wait_async(rtlsdr_dev_t *dev, rtlsdr_async_read_cb_t cb, void *ctx);
 
diff --git a/src/main.c b/src/main.c
index 4f8d064..6828c73 100644
--- a/src/main.c
+++ b/src/main.c
@@ -36,8 +36,8 @@ void usage(void)
 	printf("rtl-sdr, an I/Q recorder for RTL2832 based DVB-T receivers\n\n"
 		"Usage:\t -f frequency to tune to [Hz]\n"
 		"\t[-s samplerate (default: 2048000 Hz)]\n"
-	        "\t[-d device index (default: 0)]\n"
-	        "\t[-g tuner gain (default: 0 dB)]\n"
+		"\t[-d device index (default: 0)]\n"
+		"\t[-g tuner gain (default: 0 dB)]\n"
 		"\toutput filename\n");
 	exit(1);
 }
@@ -48,7 +48,7 @@ static void sighandler(int signum)
 	rtlsdr_cancel_async(dev);
 }
 
-void rtlsdr_callback(const char *buf, uint32_t len, void *ctx)
+void rtlsdr_callback(unsigned char *buf, uint32_t len, void *ctx)
 {
 	fwrite(buf, len, 1, (FILE*)ctx);
 }