diff --git a/src/Bloc/ByteString.extension.st b/src/Bloc/ByteString.extension.st
new file mode 100644
index 000000000..17e445d6e
--- /dev/null
+++ b/src/Bloc/ByteString.extension.st
@@ -0,0 +1,6 @@
+Extension { #name : #ByteString }
+
+{ #category : #'*Bloc' }
+ByteString >> gtCharIndexAtByteOffset: anOffset [
+	^ anOffset + 1
+]
diff --git a/src/Bloc/ByteSymbol.extension.st b/src/Bloc/ByteSymbol.extension.st
new file mode 100644
index 000000000..5137adcba
--- /dev/null
+++ b/src/Bloc/ByteSymbol.extension.st
@@ -0,0 +1,6 @@
+Extension { #name : #ByteSymbol }
+
+{ #category : #'*Bloc' }
+ByteSymbol >> gtCharIndexAtByteOffset: anOffset [
+	^ anOffset + 1
+]
diff --git a/src/Bloc/String.extension.st b/src/Bloc/String.extension.st
index eff364277..067596544 100644
--- a/src/Bloc/String.extension.st
+++ b/src/Bloc/String.extension.st
@@ -6,3 +6,8 @@ String >> asBlocElementId [
 
 	^ BlElementId named: self asSymbol
 ]
+
+{ #category : #'*Bloc' }
+String >> gtCharIndexAtByteOffset: anOffset [
+	^ self subclassResponsibility
+]
diff --git a/src/Bloc/WideString.extension.st b/src/Bloc/WideString.extension.st
new file mode 100644
index 000000000..cc3db98ce
--- /dev/null
+++ b/src/Bloc/WideString.extension.st
@@ -0,0 +1,8 @@
+Extension { #name : #WideString }
+
+{ #category : #'*Bloc' }
+WideString >> gtCharIndexAtByteOffset: anOffset [
+	<primitive: 'primitiveWideStringByteIndexToCharIndex'>
+	
+	^ self primitiveFail
+]
diff --git a/src/Bloc/WideSymbol.extension.st b/src/Bloc/WideSymbol.extension.st
new file mode 100644
index 000000000..869b4b6d0
--- /dev/null
+++ b/src/Bloc/WideSymbol.extension.st
@@ -0,0 +1,8 @@
+Extension { #name : #WideSymbol }
+
+{ #category : #'*Bloc' }
+WideSymbol >> gtCharIndexAtByteOffset: anOffset [
+	<primitive: 'primitiveWideStringByteIndexToCharIndex'>
+	
+	^ self primitiveFail
+]