diff --git a/lib/hackrf/hackrf_common.h b/lib/hackrf/hackrf_common.h
index ea093b9..bb553c3 100644
--- a/lib/hackrf/hackrf_common.h
+++ b/lib/hackrf/hackrf_common.h
@@ -34,7 +34,7 @@
 #define BUF_LEN  (16 * 32 * 512) /* must be multiple of 512 */
 #define BUF_NUM   15
 
-#define BYTES_PER_SAMPLE  2 /* HackRF device produces/consumes 8 bit unsigned IQ data */
+#define BYTES_PER_SAMPLE  2 /* HackRF device produces/consumes 8 bit signed IQ data */
 
 #define HACKRF_FORMAT_ERROR(ret, msg) \
   boost::str( boost::format(msg " (%1%) %2%") \
diff --git a/lib/hackrf/hackrf_source_c.cc b/lib/hackrf/hackrf_source_c.cc
index 4f2fb78..662d04a 100644
--- a/lib/hackrf/hackrf_source_c.cc
+++ b/lib/hackrf/hackrf_source_c.cc
@@ -88,7 +88,7 @@ hackrf_source_c::hackrf_source_c (const std::string &args)
 
   // create a lookup table for gr_complex values
   for (unsigned int i = 0; i <= 0xff; i++) {
-    _lut.push_back( float(i) * (1.0f/128.0f) );
+    _lut.push_back( float(int8_t(i)) * (1.0f/128.0f) );
   }
 
   if ( BUF_NUM != _buf_num || BUF_LEN != _buf_len ) {