diff --git a/extensions/smallrye-graphql/runtime/src/main/java/io/quarkus/smallrye/graphql/runtime/SmallRyeGraphQLExecutionHandler.java b/extensions/smallrye-graphql/runtime/src/main/java/io/quarkus/smallrye/graphql/runtime/SmallRyeGraphQLExecutionHandler.java
index b163058fee5603..43dba98ef7548b 100644
--- a/extensions/smallrye-graphql/runtime/src/main/java/io/quarkus/smallrye/graphql/runtime/SmallRyeGraphQLExecutionHandler.java
+++ b/extensions/smallrye-graphql/runtime/src/main/java/io/quarkus/smallrye/graphql/runtime/SmallRyeGraphQLExecutionHandler.java
@@ -267,10 +267,10 @@ private static String parseCharset(String mimeType) {
         if (charsetLen == 0) {
             return null;
         }
-        return charsetOf(mimeType, charsetValueStart, charsetValueEnd, charsetLen);
+        return charsetOf(mimeType, charsetValueStart, charsetLen);
     }
 
-    private static String charsetOf(String mimeType, int charsetValueStart, int charsetValueEnd, int charsetLen) {
+    private static String charsetOf(String mimeType, int charsetValueStart, int charsetLen) {
         switch (charsetLen) {
             case 5:
                 if (mimeType.regionMatches(charsetValueStart, "utf-8", 0, 5)) {
@@ -283,7 +283,7 @@ private static String charsetOf(String mimeType, int charsetValueStart, int char
                 }
                 break;
         }
-        return mimeType.substring(charsetValueStart, charsetValueEnd);
+        return mimeType.substring(charsetValueStart, charsetValueStart + charsetLen);
     }
 
     private static String getCharset(String mimeType) {