diff --git a/shared/mp3-misc.ts b/shared/mp3-misc.ts
index 9ab974a..19fd947 100644
--- a/shared/mp3-misc.ts
+++ b/shared/mp3-misc.ts
@@ -52,11 +52,11 @@ export const computeMp3FrameSize = (
 	if (layer === 0) {
 		return 0; // Not expected that this is hit
 	} else if (layer === 1) {
-		return Math.round(144 * bitrate / (sampleRate << lowSamplingFrequency)) + padding;
+		return Math.floor(144 * bitrate / (sampleRate << lowSamplingFrequency)) + padding;
 	} else if (layer === 2) {
-		return Math.round(144 * bitrate / sampleRate) + padding;
+		return Math.floor(144 * bitrate / sampleRate) + padding;
 	} else { // layer === 3
-		return (Math.round(12 * bitrate / sampleRate) + padding) * 4;
+		return (Math.floor(12 * bitrate / sampleRate) + padding) * 4;
 	}
 };
 
diff --git a/src/input-format.ts b/src/input-format.ts
index 6d9c258..5cfe902 100644
--- a/src/input-format.ts
+++ b/src/input-format.ts
@@ -289,7 +289,7 @@ export class Mp3InputFormat extends InputFormat {
 			return true;
 		}
 
-		currentPos = firstResult.startPos += firstResult.header.totalSize;
+		currentPos = firstResult.startPos + firstResult.header.totalSize;
 
 		// Fine, we found one frame header, but we're still not entirely sure this is MP3. Let's check if we can find
 		// another header right after it: