diff --git a/src/Microdown/MicAbstractCodeBlock.class.st b/src/Microdown/MicAbstractCodeBlock.class.st
index 1c08b322..8e833478 100644
--- a/src/Microdown/MicAbstractCodeBlock.class.st
+++ b/src/Microdown/MicAbstractCodeBlock.class.st
@@ -15,7 +15,7 @@ MicAbstractCodeBlock class >> alternateBlockClassFor: line [
 
 	| tag |
 	tag := ((line allButFirst: CodeblockMarkup size) 
-		        copyUpTo: $|) trimBoth.
+		        copyUpTo: $|) trimBoth asSymbol.
 	tag = #script ifTrue: [ ^ MicScriptBlock  ].
 	^ MicScriptBlock allSubclasses detect: [ :each | each tag = tag ] ifNone: [ MicCodeBlock ]
 ]
diff --git a/src/Microdown/MicArgumentList.class.st b/src/Microdown/MicArgumentList.class.st
index 7f94a8f8..c44d394c 100644
--- a/src/Microdown/MicArgumentList.class.st
+++ b/src/Microdown/MicArgumentList.class.st
@@ -116,7 +116,7 @@ MicArgumentList >> printOn: aStream [
 	self hasNonDefaultValue 
 		ifTrue:[
 			aStream nextPutAll: self defaultValue.
-			argKeys := self keys copyWithout: self defaultArg.
+			argKeys := self keys copyWithout: self defaultArg asSymbol.
 			argKeys ifNotEmpty: [aStream nextPut: $|]]
 		ifFalse: [argKeys := self keys].
 	aStream nextPutAll: ((argKeys collect: [:k| k,'=',(self at:k)]) joinUsing: '&')
diff --git a/src/Microdown/MicElement.class.st b/src/Microdown/MicElement.class.st
index 0c2c2440..69474268 100644
--- a/src/Microdown/MicElement.class.st
+++ b/src/Microdown/MicElement.class.st
@@ -36,7 +36,11 @@ MicElement class >> buildMicroDownUsing: aBuilder  withComment: aComment [
 { #category : #utilities }
 MicElement class >> extensionClassFor: tag [
 	"I am a utility method used in extension blocks to find the right subclass to instantiate"
-	^ self allSubclasses detect: [ :each | each tag = tag ] ifNone: [ self ]
+
+	| tagSymbol |
+
+	tagSymbol := tag asSymbol.
+	^ self allSubclasses detect: [ :each | each tag = tagSymbol ] ifNone: [ self ]
 ]
 
 { #category : #visiting }
diff --git a/src/Microdown/MicResourceReference.class.st b/src/Microdown/MicResourceReference.class.st
index 0b7f5c4f..f53b2c9d 100644
--- a/src/Microdown/MicResourceReference.class.st
+++ b/src/Microdown/MicResourceReference.class.st
@@ -40,7 +40,7 @@ MicResourceReference class >> fromUri: aString [
 	uri scheme
 		ifNil: [ ^ MicRelativeResourceReference new relativePath: aString ].
 	refClass := self allSubclasses 
-		detect: [ :rc | rc handlesUriScheme: uri scheme ]
+		detect: [ :rc | rc handlesUriScheme: uri scheme asString ]
 		ifNone: [ MicUnknownResourceUri ].
 	^ refClass newFromUri: uri