diff --git a/src/main/java/net/fabricmc/loom/extension/MixinExtensionApiImpl.java b/src/main/java/net/fabricmc/loom/extension/MixinExtensionApiImpl.java
index bdcf7e657..eae0061ec 100644
--- a/src/main/java/net/fabricmc/loom/extension/MixinExtensionApiImpl.java
+++ b/src/main/java/net/fabricmc/loom/extension/MixinExtensionApiImpl.java
@@ -74,9 +74,20 @@ public Property<Boolean> getUseLegacyMixinAp() {
 		return useMixinAp;
 	}
 
+	protected void checkMixinApEnabled() {
+		if (LoomGradleExtension.get(project).isForge()) {
+			// Arch: We need to access afterEvaluate state in useLegacyMixinAp's convention, so let's not query it.
+			// Otherwise, this extension can't be used in a buildscript without afterEvaluate.
+			// https://github.com/architectury/architectury-loom/issues/242
+			return;
+		}
+
+		if (!getUseLegacyMixinAp().get()) throw new IllegalStateException("You need to set useLegacyMixinAp = true to configure Mixin annotation processor.");
+	}
+
 	@Override
 	public Property<String> getRefmapTargetNamespace() {
-		if (!getUseLegacyMixinAp().get()) throw new IllegalStateException("You need to set useLegacyMixinAp = true to configure Mixin annotation processor.");
+		checkMixinApEnabled();
 
 		return refmapTargetNamespace;
 	}
diff --git a/src/main/java/net/fabricmc/loom/extension/MixinExtensionImpl.java b/src/main/java/net/fabricmc/loom/extension/MixinExtensionImpl.java
index cc8b03a6a..796b6e358 100644
--- a/src/main/java/net/fabricmc/loom/extension/MixinExtensionImpl.java
+++ b/src/main/java/net/fabricmc/loom/extension/MixinExtensionImpl.java
@@ -61,10 +61,7 @@ public MixinExtensionImpl(Project project) {
 
 	@Override
 	public Property<String> getDefaultRefmapName() {
-		// Arch: We need to access afterEvaluate state in useLegacyMixinAp's convention, so let's not query it.
-		// Otherwise, this property can't be set in a buildscript without afterEvaluate.
-		// https://github.com/architectury/architectury-loom/issues/242
-		// if (!super.getUseLegacyMixinAp().get()) throw new IllegalStateException("You need to set useLegacyMixinAp = true to configure Mixin annotation processor.");
+		checkMixinApEnabled();
 
 		return defaultRefmapName;
 	}
@@ -84,7 +81,7 @@ private String getDefaultMixinRefmapName() {
 
 	@Override
 	protected PatternSet add0(SourceSet sourceSet, Provider<String> refmapName) {
-		if (!super.getUseLegacyMixinAp().get()) throw new IllegalStateException("You need to set useLegacyMixinAp = true to configure Mixin annotation processor.");
+		checkMixinApEnabled();
 
 		PatternSet pattern = new PatternSet().setIncludes(Collections.singletonList("**/*.json"));
 		MixinExtension.setMixinInformationContainer(sourceSet, new MixinExtension.MixinInformationContainer(sourceSet, refmapName, pattern));