diff --git a/assembler.py b/assembler.py
index 727fe76..5d337a3 100644
--- a/assembler.py
+++ b/assembler.py
@@ -14,10 +14,10 @@ class FromAssemblerCallGraphBuilder(CallGraphBuilder):
 
     def __init__(self, baseDirs, specialModuleFiles = {}):
         assertType(specialModuleFiles, 'specialModuleFiles', dict)
+       
         if isinstance(baseDirs, str):
             baseDirs = [baseDirs]
         assertTypeAll(baseDirs, 'baseDirs', str)
-
         for baseDir in baseDirs:    
             if not os.path.isdir(baseDir):
                 raise IOError("Not a directory: " + baseDir);
diff --git a/source.py b/source.py
index 0bc85ea..7431354 100644
--- a/source.py
+++ b/source.py
@@ -1533,12 +1533,17 @@ def __removeStringsFromStatement(statement):
         return cleanStatement
 
 class SourceFiles(object):
-    def __init__(self, baseDir, specialModuleFiles={}):
+    def __init__(self, baseDirs, specialModuleFiles={}):
         assertType(specialModuleFiles, 'specialModuleFiles', dict)
-        if not os.path.isdir(baseDir):
-            raise IOError("Not a directory: " + baseDir)
         
-        self.__baseDir = baseDir
+        if isinstance(baseDirs, str):
+            baseDirs = [baseDirs]
+        assertTypeAll(baseDirs, 'baseDirs', str)
+        for baseDir in baseDirs:    
+            if not os.path.isdir(baseDir):
+                raise IOError("Not a directory: " + baseDir);
+        
+        self.__baseDirs = baseDirs
         self.__filesByPath = dict()
         self.__filesByModules = dict()
         self.setSpecialModuleFiles(specialModuleFiles)
@@ -1555,9 +1560,6 @@ def setSpecialModuleFiles(self, specialModuleFiles):
 
         self.__filesByModules = dict() # Clear Module Cache
         
-    def getBaseDir(self):
-        return self.__baseDir
-    
     def existsSubroutine(self, subroutineName):
         assertType(subroutineName, 'subroutineName', SubroutineName)
         
@@ -1621,8 +1623,8 @@ def getRelativePath(self, sourceFile):
         assertType(sourceFile, 'sourceFile', SourceFile)
         
         path = sourceFile.getPath()
-        if path.startswith(self.__baseDir):
-            path = path[len(self.__baseDir):].lstrip('/')
+        if path.startswith(self.__baseDirs):
+            path = path[len(self.__baseDirs):].lstrip('/')
         return path
         
     def __getModuleFileName(self, moduleName):
@@ -1632,10 +1634,11 @@ def __getModuleFileName(self, moduleName):
             return moduleName + '.f90'
         
     def __findFile(self, fileName):
-        for root, _, files in os.walk(self.__baseDir):
-            for name in files:
-                if name.replace('.F90', '.f90') == fileName.replace('.F90', '.f90'):
-                    return os.path.join(root, name)
+        for baseDir in self.__baseDirs:
+            for root, _, files in os.walk(baseDir):
+                for name in files:
+                    if name.replace('.F90', '.f90') == fileName.replace('.F90', '.f90'):
+                        return os.path.join(root, name)
         return None
     
     def clearCache(self):