diff --git a/pyro/diffusion/problems/gaussian.py b/pyro/diffusion/problems/gaussian.py
index 5ab52a10b..447d993e8 100644
--- a/pyro/diffusion/problems/gaussian.py
+++ b/pyro/diffusion/problems/gaussian.py
@@ -1,3 +1,10 @@
+"""Initialize the profile to a Gaussian.  With a constant
+conductivity, an initial Gaussian profile remains Gaussian, with the
+peak lowering and width increasing with time.  This allows this
+problem to be used for verification.
+
+"""
+
 import numpy
 
 from pyro.util import msg
diff --git a/pyro/diffusion/problems/test.py b/pyro/diffusion/problems/test.py
index b34c09a6d..8306c2213 100644
--- a/pyro/diffusion/problems/test.py
+++ b/pyro/diffusion/problems/test.py
@@ -1,3 +1,5 @@
+"""A problem setup used for unit testing."""
+
 DEFAULT_INPUTS = None
 
 PROBLEM_PARAMS = {}