diff --git a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/utils/ExternalImage.kt b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/utils/ExternalImage.kt
index 60596ac52..ef084b7b2 100644
--- a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/utils/ExternalImage.kt
+++ b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/utils/ExternalImage.kt
@@ -184,7 +184,7 @@ internal operator fun ByteArray.get(range: IntRange): String = buildString {
 
 private fun Byte.fixToString(): String {
     return when (this.toInt()) {
-        in 0..15 -> "0${this.toString(16)}"
-        else -> this.toString(16)
+        in 0..15 -> "0${this.toString(16).toUpperCase()}"
+        else -> this.toString(16).toUpperCase()
     }
 }
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