diff --git a/image/decoders/nsICODecoder.cpp b/image/decoders/nsICODecoder.cpp
index 496e16c1517..b8645de911f 100644
--- a/image/decoders/nsICODecoder.cpp
+++ b/image/decoders/nsICODecoder.cpp
@@ -27,14 +27,6 @@ static const uint32_t BITMAPINFOSIZE = bmp::InfoHeaderLength::WIN_ICO;
 // Actual Data Processing
 // ----------------------------------------
 
-uint32_t
-nsICODecoder::CalcAlphaRowSize()
-{
-  // Calculate rowsize in DWORD's and then return in # of bytes
-  uint32_t rowSize = (GetRealWidth() + 31) / 32; // + 31 to round up
-  return rowSize * 4; // Return rowSize in bytes
-}
-
 // Obtains the number of colors from the bits per pixel
 uint16_t
 nsICODecoder::GetNumColors()
diff --git a/image/decoders/nsICODecoder.h b/image/decoders/nsICODecoder.h
index 3e0d4cac57d..8dfe527b6d2 100644
--- a/image/decoders/nsICODecoder.h
+++ b/image/decoders/nsICODecoder.h
@@ -93,8 +93,6 @@ private:
   // Fixes the ICO width to match that of the BIH.
   // Returns false if invalid information is contained within.
   bool FixBitmapWidth(int8_t* bih);
-  // Calculates the row size in bytes for the AND mask table
-  uint32_t CalcAlphaRowSize();
   // Obtains the number of colors from the BPP, mBPP must be filled in
   uint16_t GetNumColors();