diff -ur adplug-2.2.1-orig/src/s3m.cpp adplug-2.2.1/src/s3m.cpp
--- adplug-2.2.1-orig/src/s3m.cpp	2016-06-12 17:19:33.369934280 +0200
+++ adplug-2.2.1/src/s3m.cpp	2016-06-12 17:32:36.190932642 +0200
@@ -25,7 +25,7 @@
 #include <cstring>
 #include "s3m.h"
 
-const char Cs3mPlayer::chnresolv[] =	// S3M -> adlib channel conversion
+const signed char Cs3mPlayer::chnresolv[] =	// S3M -> adlib channel conversion
   {-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,0,1,2,3,4,5,6,7,8,-1,-1,-1,-1,-1,-1,-1};
 
 const unsigned short Cs3mPlayer::notetable[12] =		// S3M adlib note table
diff -ur adplug-2.2.1-orig/src/s3m.h adplug-2.2.1/src/s3m.h
--- adplug-2.2.1-orig/src/s3m.h	2016-06-12 17:19:33.367934293 +0200
+++ adplug-2.2.1/src/s3m.h	2016-06-12 17:37:14.538154102 +0200
@@ -90,7 +90,7 @@
   unsigned char crow,ord,speed,tempo,del,songend,loopstart,loopcnt;
 
  private:
-  static const char chnresolv[];
+  static const signed char chnresolv[];
   static const unsigned short notetable[12];
   static const unsigned char vibratotab[32];