diff --git a/grc_tests/test_bpsk31_parts.grc b/grc_tests/test_bpsk31_parts.grc
index c44b6e2..ac3ad4d 100644
--- a/grc_tests/test_bpsk31_parts.grc
+++ b/grc_tests/test_bpsk31_parts.grc
@@ -257,7 +257,7 @@
     </param>
     <param>
       <key>commandline</key>
-      <value>csdr dsb_fc | csdr shift_addition_cc $(csdr =-2000./48e3) | csdr fir_decimate_cc 32</value>
+      <value>csdr dsb_fc | csdr shift_addition_cc $(csdr =-2000./48e3) | csdr fir_decimate_cc 32 | csdr simple_agc_cc 0.0001 0.5</value>
     </param>
     <param>
       <key>comment</key>
diff --git a/libcsdr.c b/libcsdr.c
index 93e3a51..d63984f 100755
--- a/libcsdr.c
+++ b/libcsdr.c
@@ -1685,6 +1685,7 @@ unsigned char differential_codec(unsigned char* input, unsigned char* output, in
 			if(!input[i]) state=!state;
 			output[i] = state;
 		}
+	return state;
 }
 
 /*