--- a/dom/media/AudioConfig.cpp
+++ b/dom/media/AudioConfig.cpp
@@ -235,26 +235,27 @@ AudioConfig::ChannelLayout::SMPTEDefault
     case L3F3R_LFE_MAP: return L3F3R_LFE;
     case L3F4_LFE_MAP: return L3F4_LFE;
     default:
       break;
   }
   AutoTArray<Channel, MAX_AUDIO_CHANNELS> layout;
   uint32_t channels = 0;
 
-  uint32_t i = 1;
+  uint32_t i = 0;
   while (aMap) {
     if (aMap & 1) {
       layout.AppendElement(static_cast<Channel>(i));
       channels++;
       if (channels > MAX_AUDIO_CHANNELS) {
         return ChannelLayout();
       }
     }
     aMap >>= 1;
+    i++;
   }
   return ChannelLayout(channels, layout.Elements());
 }
 
 bool
 AudioConfig::ChannelLayout::MappingTable(const ChannelLayout& aOther,
                                          uint8_t* aMap) const
 {