diff --git a/src/main/java/net/fabricmc/loom/task/service/TinyRemapperService.java b/src/main/java/net/fabricmc/loom/task/service/TinyRemapperService.java
index 780c8acc..f3643064 100644
--- a/src/main/java/net/fabricmc/loom/task/service/TinyRemapperService.java
+++ b/src/main/java/net/fabricmc/loom/task/service/TinyRemapperService.java
@@ -76,7 +76,7 @@ public class TinyRemapperService implements SharedService {
 			mappings.add(MappingsService.createDefault(project, from, to).getMappingsProvider());
 
 			if (legacyMixin) {
-				mappings.add(MixinMappingsService.getService(SharedServiceManager.get(project)).getMappingProvider(from, to));
+				mappings.add(MixinMappingsService.getService(SharedServiceManager.get(project)).getMappingProvider(from, extension.isForge() && to.equals("srg") ? "intermediary" : to));
 			}
 
 			return new TinyRemapperService(mappings, !legacyMixin, useKotlinExtension);
diff --git a/src/main/java/net/fabricmc/loom/util/TinyRemapperHelper.java b/src/main/java/net/fabricmc/loom/util/TinyRemapperHelper.java
index 8e34f9ee..6465c45d 100644
--- a/src/main/java/net/fabricmc/loom/util/TinyRemapperHelper.java
+++ b/src/main/java/net/fabricmc/loom/util/TinyRemapperHelper.java
@@ -48,6 +48,7 @@ import net.fabricmc.loom.api.mappings.layered.MappingsNamespace;
 import net.fabricmc.loom.util.srg.InnerClassRemapper;
 import net.fabricmc.mappingio.MappingReader;
 import net.fabricmc.mappingio.tree.MappingTree;
+import net.fabricmc.mappingio.tree.MappingTreeView;
 import net.fabricmc.mappingio.tree.MemoryMappingTree;
 
 /**
@@ -160,6 +161,10 @@ public final class TinyRemapperHelper {
 			final int fromId = mappings.getNamespaceId(from);
 			final int toId = mappings.getNamespaceId(to);
 
+			if (toId == MappingTreeView.NULL_NAMESPACE_ID) {
+				System.out.println("Warning: Trying to remap to unknown namespace: " + to);
+			}
+
 			for (MappingTree.ClassMapping classDef : mappings.getClasses()) {
 				String className = classDef.getName(fromId);
 				String dstName = classDef.getName(toId);