diff --git a/bootstrap-dev/src/main/java/org/spongepowered/bootstrap/dev/SourceSet.java b/bootstrap-dev/src/main/java/org/spongepowered/bootstrap/dev/SourceSet.java
index 540c752afcc..badeb5407dc 100644
--- a/bootstrap-dev/src/main/java/org/spongepowered/bootstrap/dev/SourceSet.java
+++ b/bootstrap-dev/src/main/java/org/spongepowered/bootstrap/dev/SourceSet.java
@@ -29,7 +29,7 @@
 import java.util.ArrayList;
 import java.util.List;
 
-public record SourceSet(String project, String name, String format) {
+public record SourceSet(Path project, String name, String format) {
 
     @Override
     public String toString() {
@@ -57,32 +57,34 @@ public static SourceSet identify(Path path) {
         }
 
         // from right to left
-        final List<String> parts = new ArrayList<>();
+        final List<String> names = new ArrayList<>();
+        final List<Path> paths = new ArrayList<>();
         while (path != null) {
-            parts.add(path.getFileName().toString());
-            if (parts.size() >= 5) {
+            names.add(path.getFileName().toString());
+            paths.add(path);
+            if (names.size() >= 5) {
                 break;
             }
             path = path.getParent();
         }
 
-        if (parts.size() >= 4 && (parts.get(0).equals("classes") || parts.get(0).equals("resources"))) {
-            final String name = parts.get(1);
-            return new SourceSet(parts.get(3), name.equals("production") ? "main" : name, "IntelliJ");
+        if (names.size() >= 4 && (names.get(0).equals("classes") || names.get(0).equals("resources"))) {
+            final String name = names.get(1);
+            return new SourceSet(paths.get(3), name.equals("production") ? "main" : name, "IntelliJ");
         }
 
-        if (parts.size() >= 4 && (parts.get(1).equals("resources") || parts.get(1).equals("generated"))) {
-            return new SourceSet(parts.get(3), parts.get(0), "Gradle");
+        if (names.size() >= 4 && (names.get(1).equals("resources") || names.get(1).equals("generated"))) {
+            return new SourceSet(paths.get(3), names.get(0), "Gradle");
         }
 
-        if (parts.size() >= 5 && parts.get(2).equals("classes")) {
-            return new SourceSet(parts.get(4), parts.get(0), "Gradle");
+        if (names.size() >= 5 && names.get(2).equals("classes")) {
+            return new SourceSet(paths.get(4), names.get(0), "Gradle");
         }
 
-        if (parts.size() >= 3 && parts.get(1).equals("bin")) {
-            return new SourceSet(parts.get(2), parts.get(0), "Eclipse");
+        if (names.size() >= 3 && names.get(1).equals("bin")) {
+            return new SourceSet(paths.get(2), names.get(0), "Eclipse");
         }
 
-        return new SourceSet("", parts.get(0), "Unknown");
+        return new SourceSet(paths.get(0), "?", "Unknown");
     }
 }
diff --git a/bootstrap-dev/src/main/java/org/spongepowered/bootstrap/dev/SpongeDevClasspathFixer.java b/bootstrap-dev/src/main/java/org/spongepowered/bootstrap/dev/SpongeDevClasspathFixer.java
index 1fc983100b0..ab566c5f915 100644
--- a/bootstrap-dev/src/main/java/org/spongepowered/bootstrap/dev/SpongeDevClasspathFixer.java
+++ b/bootstrap-dev/src/main/java/org/spongepowered/bootstrap/dev/SpongeDevClasspathFixer.java
@@ -29,6 +29,7 @@
 import java.io.File;
 import java.nio.file.Files;
 import java.nio.file.Path;
+import java.nio.file.Paths;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Set;
@@ -49,6 +50,7 @@ public String name() {
      */
     @Override
     public boolean process(final List<Path[]> classpath) {
+        final Path spongeRoot = Paths.get(System.getProperty("sponge.dev.root")).toAbsolutePath();
         final Set<String> ignoredLibs = Set.of("bootstrap-dev.jar");
         final Set<String> bootLibs = Set.of(System.getProperty("sponge.dev.boot").split(File.pathSeparator));
         final Set<String> gameShadedLibs = Set.of(System.getProperty("sponge.dev.gameShaded").split(File.pathSeparator));
@@ -70,46 +72,55 @@ public boolean process(final List<Path[]> classpath) {
             final Path path = paths[0];
             final SourceSet sourceSet = SourceSet.identify(path);
             if (sourceSet != null) {
-                if (DEBUG) {
-                    System.out.println("SourceSet (" + sourceSet + "): " + path);
-                }
+                if (sourceSet.project().startsWith(spongeRoot)) {
+                    if (DEBUG) {
+                        System.out.println("Sponge SourceSet (" + sourceSet + "): " + path);
+                    }
 
-                switch (sourceSet.project()) {
-                    case "bootstrap-dev":
-                        // ignore
-                        break;
-                    case "modlauncher-transformers", "library-manager":
-                        bootUnions.add(sourceSet.project(), path);
-                        break;
-                    case "SpongeAPI":
-                        switch (sourceSet.name()) {
-                            case "ap":
-                                // ignore
-                                break;
-                            case "main":
-                                hasAPISourceSet.set(true);
-                                // no break
-                            default:
-                                unions.add("sponge", path);
-                                break;
-                        }
-                        break;
-                    case "Sponge", "vanilla", "forge":
-                        switch (sourceSet.name()) {
-                            case "applaunch":
-                                bootUnions.add("applaunch", path);
-                                break;
-                            case "lang":
-                                unions.add("lang", path);
-                                break;
-                            default:
-                                unions.add("sponge", path);
-                                break;
-                        }
-                        break;
-                    default:
-                        unions.add(sourceSet.project(), path);
-                        break;
+                    final String projectName = spongeRoot.relativize(sourceSet.project()).toString();
+                    switch (projectName) {
+                        case "bootstrap-dev":
+                            // ignore
+                            break;
+                        case "modlauncher-transformers", "library-manager":
+                            bootUnions.add(projectName, path);
+                            break;
+                        case "SpongeAPI":
+                            switch (sourceSet.name()) {
+                                case "ap":
+                                    // ignore
+                                    break;
+                                case "main":
+                                    hasAPISourceSet.set(true);
+                                    // no break
+                                default:
+                                    unions.add("sponge", path);
+                                    break;
+                            }
+                            break;
+                        case "", "vanilla", "forge":
+                            switch (sourceSet.name()) {
+                                case "applaunch":
+                                    bootUnions.add("applaunch", path);
+                                    break;
+                                case "lang":
+                                    unions.add("lang", path);
+                                    break;
+                                default:
+                                    unions.add("sponge", path);
+                                    break;
+                            }
+                            break;
+                        default:
+                            unions.add(projectName, path);
+                            break;
+                    }
+                } else {
+                    if (DEBUG) {
+                        System.out.println("External SourceSet (" + sourceSet + "): " + path);
+                    }
+
+                    unions.add(sourceSet.project().toString(), path);
                 }
                 return true;
             }
diff --git a/forge/build.gradle.kts b/forge/build.gradle.kts
index b3a90619a7b..c973f13168e 100644
--- a/forge/build.gradle.kts
+++ b/forge/build.gradle.kts
@@ -247,6 +247,7 @@ afterEvaluate {
         val bootFileNames = spongeImpl.buildRuntimeFileNames(serviceLayerConfig.get()) // service in boot during dev
         val gameShadedFileNames = spongeImpl.buildRuntimeFileNames(gameShadedLibrariesConfig.get())
         runs.configureEach {
+            jvmArgs("-Dsponge.dev.root=" + project.rootDir)
             jvmArgs("-Dsponge.dev.boot=$bootFileNames")
             jvmArgs("-Dsponge.dev.gameShaded=$gameShadedFileNames")
         }
diff --git a/vanilla/build.gradle.kts b/vanilla/build.gradle.kts
index 90595bb3a29..27fc697f86c 100644
--- a/vanilla/build.gradle.kts
+++ b/vanilla/build.gradle.kts
@@ -301,6 +301,7 @@ minecraft {
             // jvmArgs("-Dbsl.debug=true") // Uncomment to debug bootstrap classpath
             mainClass("net.minecraftforge.bootstrap.ForgeBootstrap")
 
+            jvmArgs("-Dsponge.dev.root=" + project.rootDir)
             jvmArgs("-Dsponge.dev.boot=$bootFileNames")
             jvmArgs("-Dsponge.dev.gameShaded=$gameShadedFileNames")
         }