diff --git a/tests/_build/README.md b/tests/_build/README.md
index fe1661a0..92985409 100644
--- a/tests/_build/README.md
+++ b/tests/_build/README.md
@@ -10,6 +10,8 @@ Output files will be placed in the "res/output" folder.
 
 Emscripten
 ----------
+On Linux, do `source ~/emsdk/emsdk_env.sh` before compiling.
+
 On Windows, you need to move into the build and run emsdk_env.bat from a command prompt using an absolute
 path like "C:\emsdk\emsdk_env.bat". Note that PowerShell doesn't work for me for some reason. Example: