diff --git a/Cantera/src/base/ct2ctml.cpp b/Cantera/src/base/ct2ctml.cpp
index 4064ed126..e3ac5eb37 100644
--- a/Cantera/src/base/ct2ctml.cpp
+++ b/Cantera/src/base/ct2ctml.cpp
@@ -61,14 +61,19 @@ namespace ctml {
   static string pypath() {
     string s = "python";
     const char* py = getenv("PYTHON_CMD");
+
+    // Try to source the "setup_cantera" script from the user's home
+    // directory in order to set PYTHON_CMD.
     if (!py) {
       const char* hm = getenv("HOME");
-      string home = stripws(string(hm));
-      string cmd = string(". ")+home
-	+string("/setup_cantera &> /dev/null");
+      if (hm) {
+        string home = stripws(string(hm));
+        string cmd = string(". ") + home
+            +string("/setup_cantera &> /dev/null");
       system(cmd.c_str());
+      }
       py = getenv("PYTHON_CMD");
-    }        
+    }
     if (py) {
       string sp = stripws(string(py));
       if (sp.size() > 0) {