diff --git a/src/Bloc/ByteString.extension.st b/src/Bloc/ByteString.extension.st
index 17e445d6e..2d643a7ef 100644
--- a/src/Bloc/ByteString.extension.st
+++ b/src/Bloc/ByteString.extension.st
@@ -2,5 +2,5 @@ Extension { #name : #ByteString }
 
 { #category : #'*Bloc' }
 ByteString >> gtCharIndexAtByteOffset: anOffset [
-	^ anOffset + 1
+	^ (anOffset + 1) min: self size
 ]
diff --git a/src/Bloc/ByteSymbol.extension.st b/src/Bloc/ByteSymbol.extension.st
index 5137adcba..69206cdde 100644
--- a/src/Bloc/ByteSymbol.extension.st
+++ b/src/Bloc/ByteSymbol.extension.st
@@ -2,5 +2,5 @@ Extension { #name : #ByteSymbol }
 
 { #category : #'*Bloc' }
 ByteSymbol >> gtCharIndexAtByteOffset: anOffset [
-	^ anOffset + 1
+	^ (anOffset + 1) min: self size
 ]