diff --git a/src/main/java/net/fabricmc/loader/api/MappingResolver.java b/src/main/java/net/fabricmc/loader/api/MappingResolver.java
index 0cea14875..8d80f3ad0 100644
--- a/src/main/java/net/fabricmc/loader/api/MappingResolver.java
+++ b/src/main/java/net/fabricmc/loader/api/MappingResolver.java
@@ -49,7 +49,7 @@ public interface MappingResolver {
 	 * Map a class name to the mapping currently used at runtime.
 	 *
 	 * @param namespace the namespace of the provided class name
-	 * @param className the provided binary class name
+	 * @param className the provided internal/binary class name
 	 * @return the mapped class name, or {@code className} if no such mapping is present
 	 */
 	String mapClassName(String namespace, String className);
@@ -58,7 +58,7 @@ public interface MappingResolver {
 	 * Unmap a class name to the mapping currently used at runtime.
 	 *
 	 * @param targetNamespace The target namespace for unmapping.
-	 * @param className the provided binary class name of the mapping form currently used at runtime
+	 * @param className the provided internal/binary class name of the mapping form currently used at runtime
 	 * @return the mapped class name, or {@code className} if no such mapping is present
 	 */
 	String unmapClassName(String targetNamespace, String className);
@@ -67,7 +67,7 @@ public interface MappingResolver {
 	 * Map a field name to the mapping currently used at runtime.
 	 *
 	 * @param namespace the namespace of the provided field name and descriptor
-	 * @param owner the binary name of the owner class of the field
+	 * @param owner the internal/binary name of the owner class of the field
 	 * @param name the name of the field
 	 * @param descriptor the descriptor of the field
 	 * @return the mapped field name, or {@code name} if no such mapping is present
@@ -78,7 +78,7 @@ public interface MappingResolver {
 	 * Map a method name to the mapping currently used at runtime.
 	 *
 	 * @param namespace the namespace of the provided method name and descriptor
-	 * @param owner the binary name of the owner class of the method
+	 * @param owner the internal/binary name of the owner class of the method
 	 * @param name the name of the method
 	 * @param descriptor the descriptor of the method
 	 * @return the mapped method name, or {@code name} if no such mapping is present
diff --git a/src/main/java/net/fabricmc/loader/impl/MappingResolverImpl.java b/src/main/java/net/fabricmc/loader/impl/MappingResolverImpl.java
index f1407bb8c..d8a591218 100644
--- a/src/main/java/net/fabricmc/loader/impl/MappingResolverImpl.java
+++ b/src/main/java/net/fabricmc/loader/impl/MappingResolverImpl.java
@@ -57,16 +57,15 @@ protected final NamespaceData getNamespaceData(String namespace) {
 
 			NamespaceData data = new NamespaceData();
 			TinyTree mappings = mappingsSupplier.get();
-			Map<String, String> classNameMap = new HashMap<>();
 
 			for (ClassDef classEntry : mappings.getClasses()) {
-				String fromClass = mapClassName(classNameMap, classEntry.getName(fromNamespace));
-				String toClass = mapClassName(classNameMap, classEntry.getName(targetNamespace));
+				String fromClass = classEntry.getName(fromNamespace);
+				String toClass = classEntry.getName(targetNamespace);
 
 				data.classNames.put(fromClass, toClass);
 				data.classNamesInverse.put(toClass, fromClass);
 
-				String mappedClassName = mapClassName(classNameMap, fromClass);
+				String mappedClassName = fromClass;
 
 				recordMember(fromNamespace, classEntry.getFields(), data.fieldNames, mappedClassName);
 				recordMember(fromNamespace, classEntry.getMethods(), data.methodNames, mappedClassName);
@@ -76,14 +75,6 @@ protected final NamespaceData getNamespaceData(String namespace) {
 		});
 	}
 
-	private static String replaceSlashesWithDots(String cname) {
-		return cname.replace('/', '.');
-	}
-
-	private String mapClassName(Map<String, String> classNameMap, String s) {
-		return classNameMap.computeIfAbsent(s, MappingResolverImpl::replaceSlashesWithDots);
-	}
-
 	private <T extends Descriptored> void recordMember(String fromNamespace, Collection<T> descriptoredList, Map<EntryTriple, String> putInto, String fromClass) {
 		for (T descriptored : descriptoredList) {
 			EntryTriple fromEntry = new EntryTriple(fromClass, descriptored.getName(fromNamespace), descriptored.getDescriptor(fromNamespace));
@@ -103,36 +94,28 @@ public String getCurrentRuntimeNamespace() {
 
 	@Override
 	public String mapClassName(String namespace, String className) {
-		if (className.indexOf('/') >= 0) {
-			throw new IllegalArgumentException("Class names must be provided in dot format: " + className);
-		}
+		className = className.replace('.', '/'); // maintain backwards compatibility with dotty format requirement
 
 		return getNamespaceData(namespace).classNames.getOrDefault(className, className);
 	}
 
 	@Override
 	public String unmapClassName(String namespace, String className) {
-		if (className.indexOf('/') >= 0) {
-			throw new IllegalArgumentException("Class names must be provided in dot format: " + className);
-		}
+		className = className.replace('.', '/'); // maintain backwards compatibility with dotty format requirement
 
 		return getNamespaceData(namespace).classNamesInverse.getOrDefault(className, className);
 	}
 
 	@Override
 	public String mapFieldName(String namespace, String owner, String name, String descriptor) {
-		if (owner.indexOf('/') >= 0) {
-			throw new IllegalArgumentException("Class names must be provided in dot format: " + owner);
-		}
+		owner = owner.replace('.', '/'); // maintain backwards compatibility with dotty format requirement
 
 		return getNamespaceData(namespace).fieldNames.getOrDefault(new EntryTriple(owner, name, descriptor), name);
 	}
 
 	@Override
 	public String mapMethodName(String namespace, String owner, String name, String descriptor) {
-		if (owner.indexOf('/') >= 0) {
-			throw new IllegalArgumentException("Class names must be provided in dot format: " + owner);
-		}
+		owner = owner.replace('.', '/'); // maintain backwards compatibility with dotty format requirement
 
 		return getNamespaceData(namespace).methodNames.getOrDefault(new EntryTriple(owner, name, descriptor), name);
 	}