diff --git a/README.md b/README.md
index cdc1718..aff3408 100644
--- a/README.md
+++ b/README.md
@@ -16,11 +16,12 @@ ODK XLSForm Offline is part of Open Data Kit (ODK), a free and open-source set o
 ## Prerequisites
 
 1. Install [Python 2.7](https://www.python.org/downloads/)
-    * If you are on Windows, you must install the 32 bit version.
+	* Windows: Use the 32 bit version.
 1. Install Python packages: ``pip install pyinstaller wxpython pyxform``
+	* macOS: Use the default Python. virtualenvs will not work.
 1. Install packaging utilities
-    * macOS: ``brew install unix2dos``
-    * Windows: [upx](https://upx.github.io/)
+	* macOS: ``brew install unix2dos``
+	* Windows: [upx](https://upx.github.io/)
 
 ## Run
 
diff --git a/requirements.txt b/requirements.txt
new file mode 100644
index 0000000..68b6902
--- /dev/null
+++ b/requirements.txt
@@ -0,0 +1,4 @@
+# macOS: Use the default Python. virtualenvs will not work.
+pyinstaller==3.4.0
+wxpython==4.0.3
+pyxform==0.12.0
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