diff --git a/src/Generator/Driver.cs b/src/Generator/Driver.cs
index fbd71357..c62b558c 100644
--- a/src/Generator/Driver.cs
+++ b/src/Generator/Driver.cs
@@ -85,6 +85,7 @@ namespace Cxxi
                 Transform.Preprocess(Library);
 
             var passes = new PassBuilder(Library);
+            passes.CleanUnit();
             passes.SortDeclarations();
             passes.ResolveIncompleteDecls(TypeDatabase);
             passes.CheckFlagEnums();
diff --git a/src/Generator/Passes/CleanUnitPass.cs b/src/Generator/Passes/CleanUnitPass.cs
new file mode 100644
index 00000000..23132a0e
--- /dev/null
+++ b/src/Generator/Passes/CleanUnitPass.cs
@@ -0,0 +1,45 @@
+namespace Cxxi.Passes
+{
+    public class CleanUnitPass : TranslationUnitPass
+    {
+        public DriverOptions Options;
+        public PassBuilder Passes;
+
+        public override bool VisitTranslationUnit(TranslationUnit unit)
+        {
+            // Try to get an include path that works from the original include
+            // directories paths.
+
+            unit.IncludePath = GetIncludePath(unit.FilePath);
+            return true;
+        }
+
+        string GetIncludePath(string filePath)
+        {
+            var includePath = filePath;
+            var shortestIncludePath = filePath;
+
+            foreach (var path in Options.IncludeDirs)
+            {
+                int idx = filePath.IndexOf(path, System.StringComparison.Ordinal);
+                if (idx == -1) continue;
+
+                string inc = filePath.Substring(path.Length);
+
+                if (inc.Length < includePath.Length && inc.Length < shortestIncludePath.Length)
+                    shortestIncludePath = inc;
+            }
+
+            return Options.IncludePrefix + shortestIncludePath.TrimStart(new char[] { '\\', '/' });
+        }
+    }
+
+    public static class CleanUnitPassExtensions
+    {
+        public static void CleanUnit(this PassBuilder builder)
+        {
+            var pass = new CleanUnitPass();
+            builder.AddPass(pass);
+        }
+    }
+}
\ No newline at end of file