diff --git a/src/osgDB/ConvertBase64.cpp b/src/osgDB/ConvertBase64.cpp
index 8a2f59e5a..7cffbefbd 100644
--- a/src/osgDB/ConvertBase64.cpp
+++ b/src/osgDB/ConvertBase64.cpp
@@ -28,7 +28,7 @@ namespace osgDB
 
     int base64_decode_value(char value_in)
     {
-        static const char decoding[] = {62,-1,-1,-1,63,52,53,54,55,56,57,58,59,60,61,-1,-1,-1,-2,-1,-1,-1,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,-1,-1,-1,-1,-1,-1,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51};
+        static const signed char decoding[] = {62,-1,-1,-1,63,52,53,54,55,56,57,58,59,60,61,-1,-1,-1,-2,-1,-1,-1,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,-1,-1,-1,-1,-1,-1,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51};
         static const char decoding_size = sizeof(decoding);
         value_in -= 43;
         if (value_in < 0 || value_in >= decoding_size) return -1;
diff --git a/src/osgPlugins/osgjs/Base64 b/src/osgPlugins/osgjs/Base64
index 6d1becc1c..acac893fc 100644
--- a/src/osgPlugins/osgjs/Base64
+++ b/src/osgPlugins/osgjs/Base64
@@ -61,7 +61,7 @@ namespace base64
   extern const char* to_table;
   extern const char* to_table_end;
 
-  extern const char* from_table;
+  extern const signed char* from_table;
 
 
   template <class InputIterator, class OutputIterator>
diff --git a/src/osgPlugins/osgjs/Base64.cpp b/src/osgPlugins/osgjs/Base64.cpp
index 227b6b1a3..73e2e1f5e 100644
--- a/src/osgPlugins/osgjs/Base64.cpp
+++ b/src/osgPlugins/osgjs/Base64.cpp
@@ -18,7 +18,7 @@ namespace base64
   const char* to_table_end =
     _to_table + sizeof(_to_table);
 
-  const char _from_table[128] =
+  const signed char _from_table[128] =
   {
     -1, -1, -1, -1, -1, -1, -1, -1, // 0
     -1, -1, -1, -1, -1, -1, -1, -1, // 8
@@ -37,6 +37,6 @@ namespace base64
     41, 42, 43, 44, 45, 46, 47, 48, // 112
     49, 50, 51, -1, -1, -1, -1, -1  // 120
   };
-  const char* from_table = _from_table;
+  const signed char* from_table = _from_table;
 }