diff --git a/libPCMutils/src/pcmdmx_lib.cpp b/libPCMutils/src/pcmdmx_lib.cpp
index 2070dbc..534acad 100644
--- a/libPCMutils/src/pcmdmx_lib.cpp
+++ b/libPCMutils/src/pcmdmx_lib.cpp
@@ -583,6 +583,8 @@ static PCMDMX_ERROR getChannelMode(
         (channelType[ch] & 0x0F) - 1,
         0); /* Assign all undefined channels (ACT_NONE) to front channels. */
 
+    if (channelIndices[ch] >= numCh[channelType[ch] >> 4][chGrp])
+      return PCMDMX_INVALID_CH_CONFIG;
     spkrPos[ch] = getSpeakerPos(channelType[ch], channelIndices[ch],
                                 numCh[channelType[ch] >> 4][chGrp]);