diff --git a/src/read.c b/src/read.c
index e45db4e..0ddb05a 100644
--- a/src/read.c
+++ b/src/read.c
@@ -945,7 +945,7 @@ static avifResult avifDecoderItemMaxExtent(const avifDecoderItem * item, const a
                     return AVIF_RESULT_BMFF_PARSE_FAILED;
                 }
                 startOffset += remainingOffset;
-                extentSize -= remainingOffset;
+                extentSize -= (size_t)remainingOffset;
                 remainingOffset = 0;
             }
         }
@@ -3147,7 +3147,7 @@ static avifResult avifDecoderPrepareSample(avifDecoder * decoder, avifDecodeSamp
             if ((decoder->io->sizeHint > 0) && (sample->offset > decoder->io->sizeHint)) {
                 return AVIF_RESULT_BMFF_PARSE_FAILED;
             }
-            avifResult readResult = decoder->io->read(decoder->io, 0, sample->offset, bytesToRead, &sampleContents);
+            avifResult readResult = decoder->io->read(decoder->io, 0, (size_t)sample->offset, bytesToRead, &sampleContents);
             if (readResult != AVIF_RESULT_OK) {
                 return readResult;
             }