diff --git a/src/main/java/net/fabricmc/loom/util/srg/InnerClassRemapper.java b/src/main/java/net/fabricmc/loom/util/srg/InnerClassRemapper.java
index 7d57f6fd..33c18701 100644
--- a/src/main/java/net/fabricmc/loom/util/srg/InnerClassRemapper.java
+++ b/src/main/java/net/fabricmc/loom/util/srg/InnerClassRemapper.java
@@ -1,5 +1,6 @@
 package net.fabricmc.loom.util.srg;
 
+import net.fabricmc.mapping.tree.ClassDef;
 import net.fabricmc.mapping.tree.TinyTree;
 import net.fabricmc.tinyremapper.IMappingProvider;
 import org.zeroturnaround.zip.ZipUtil;
@@ -8,49 +9,43 @@ import java.io.IOException;
 import java.io.InputStream;
 import java.nio.file.Files;
 import java.nio.file.Path;
-import java.util.HashMap;
 import java.util.Map;
-import java.util.Objects;
-import java.util.Set;
+import java.util.function.BiConsumer;
 import java.util.stream.Collectors;
 
 public class InnerClassRemapper {
 	public static IMappingProvider of(Path fromJar, TinyTree mappingsWithSrg, String from, String to) throws IOException {
-		Map<String, String> map = buildInnerClassRemap(fromJar, mappingsWithSrg, from, to);
 		return sink -> {
-			for (Map.Entry<String, String> entry : map.entrySet()) {
-				sink.acceptClass(entry.getKey(), entry.getValue());
-			}
+			remapInnerClass(fromJar, mappingsWithSrg, from, to, sink::acceptClass);
 		};
 	}
 
-	private static Map<String, String> buildInnerClassRemap(Path fromJar, TinyTree mappingsWithSrg, String from, String to) throws IOException {
-		Map<String, String> remapInnerClasses = new HashMap<>();
-
+	private static void remapInnerClass(Path fromJar, TinyTree mappingsWithSrg, String from, String to, BiConsumer<String, String> action) {
 		try (InputStream inputStream = Files.newInputStream(fromJar)) {
-			Set<String> availableClasses = mappingsWithSrg.getClasses().stream()
-					.map(classDef -> classDef.getName(from))
-					.collect(Collectors.toSet());
+			Map<String, String> availableClasses = mappingsWithSrg.getClasses().stream()
+					.collect(Collectors.groupingBy(classDef -> classDef.getName(from),
+							Collectors.<ClassDef, String>reducing(
+									null,
+									classDef -> classDef.getName(to),
+									(first, last) -> last
+							))
+					);
 			ZipUtil.iterate(inputStream, (in, zipEntry) -> {
 				if (!zipEntry.isDirectory() && zipEntry.getName().contains("$") && zipEntry.getName().endsWith(".class")) {
 					String className = zipEntry.getName().substring(0, zipEntry.getName().length() - 6);
-					if (!availableClasses.contains(className)) {
+					if (!availableClasses.containsKey(className)) {
 						String parentName = className.substring(0, className.indexOf('$'));
 						String childName = className.substring(className.indexOf('$') + 1);
-						String remappedParentName = mappingsWithSrg.getClasses().stream()
-								.filter(classDef -> Objects.equals(classDef.getName(from), parentName))
-								.findFirst()
-								.map(classDef -> classDef.getName(to))
-								.orElse(parentName);
+						String remappedParentName = availableClasses.getOrDefault(parentName, parentName);
 						String remappedName = remappedParentName + "$" + childName;
 						if (!className.equals(remappedName)) {
-							remapInnerClasses.put(className, remappedName);
+							action.accept(className, remappedName);
 						}
 					}
 				}
 			});
+		} catch (IOException e) {
+			throw new RuntimeException(e);
 		}
-
-		return remapInnerClasses;
 	}
 }