--- a/Base64Coder.st	Fri Mar 22 13:45:55 2019 +0100
+++ b/Base64Coder.st	Fri Mar 22 13:56:20 2019 +0100
@@ -444,7 +444,7 @@
     
     if ((argIsString || __isByteArray(aStringOrByteArray))
      && __isStringLike(mapping)) {
-        unsigned char *_mapping = __stringVal(mapping);;
+        unsigned char *__mapping = __stringVal(mapping);;
         int numInChars;
         unsigned char *in;
         unsigned char quickBuffer[N_QUICKBUFFER+5];
@@ -498,17 +498,17 @@
             }
 #ifdef __LSBFIRST__
             {
-                unsigned int out = _mapping[(charBuffer >> 18) & 0x3F];
-                out |= (_mapping[(charBuffer >> 12) & 0x3F]) << 8;
-                out |= (_mapping[(charBuffer >> 6) & 0x3F]) << 16;
-                out |= (_mapping[(charBuffer) & 0x3F]) << 24;
+                unsigned int out = __mapping[(charBuffer >> 18) & 0x3F];
+                out |= (__mapping[(charBuffer >> 12) & 0x3F]) << 8;
+                out |= (__mapping[(charBuffer >> 6) & 0x3F]) << 16;
+                out |= (__mapping[(charBuffer) & 0x3F]) << 24;
                 ((unsigned int*)(&buffer[outLen]))[0] = out;
             }
 #else
-            buffer[outLen] = _mapping[(charBuffer >> 18) & 0x3F];
-            buffer[outLen+1] = _mapping[(charBuffer >> 12) & 0x3F];
-            buffer[outLen+2] = _mapping[(charBuffer >> 6) & 0x3F];
-            buffer[outLen+3] = _mapping[(charBuffer) & 0x3F];
+            buffer[outLen] = __mapping[(charBuffer >> 18) & 0x3F];
+            buffer[outLen+1] = __mapping[(charBuffer >> 12) & 0x3F];
+            buffer[outLen+2] = __mapping[(charBuffer >> 6) & 0x3F];
+            buffer[outLen+3] = __mapping[(charBuffer) & 0x3F];
 #endif
             outLen += 4;
             lineLength += 4;
@@ -526,10 +526,10 @@
                 
                 // pad with '=='
                 charBuffer = (in[i]) << 4;    
-                buffer[outLen] = _mapping[(charBuffer >> 6) & 0x3F];
-                buffer[outLen+1] = _mapping[(charBuffer) & 0x3F];
-                buffer[outLen+2] = _mapping[64];
-                buffer[outLen+3] = _mapping[64];
+                buffer[outLen] = __mapping[(charBuffer >> 6) & 0x3F];
+                buffer[outLen+1] = __mapping[(charBuffer) & 0x3F];
+                buffer[outLen+2] = __mapping[64];
+                buffer[outLen+3] = __mapping[64];
                 outLen += 4;
             } else {
                 unsigned int charBuffer;
@@ -539,10 +539,10 @@
                 charBuffer = (in[i]) << 8;    
                 charBuffer |= (in[i+1]); 
                 charBuffer <<= 2;
-                buffer[outLen] = _mapping[(charBuffer >> 12) & 0x3F];
-                buffer[outLen+1] = _mapping[(charBuffer >> 6) & 0x3F];
-                buffer[outLen+2] = _mapping[(charBuffer) & 0x3F];
-                buffer[outLen+3] = _mapping[64];
+                buffer[outLen] = __mapping[(charBuffer >> 12) & 0x3F];
+                buffer[outLen+1] = __mapping[(charBuffer >> 6) & 0x3F];
+                buffer[outLen+2] = __mapping[(charBuffer) & 0x3F];
+                buffer[outLen+3] = __mapping[64];
                 outLen += 4;
             }    
         }