diff --git a/cmake/modules/AutoGenGo.cmake b/cmake/modules/AutoGenGo.cmake
index 7c59578..a17b62a 100644
--- a/cmake/modules/AutoGenGo.cmake
+++ b/cmake/modules/AutoGenGo.cmake
@@ -434,7 +434,11 @@
   get_filename_component(outfile "${outpath}" NAME)
   get_filename_component(outdir "${outpath}" DIRECTORY)
   set(tmpfile "${outdir}/tmp-${outfile}")
-  set(shell $ENV{SHELL})
+  if(DEFINED ENV{SHELL})
+    set(shell $ENV{SHELL})
+  else()
+    set(shell "/bin/bash")
+  endif()
 
   # Create a rule that runs the script into a temporary file.
   if( NOT ARG_CAPTURE )
diff --git a/cmake/modules/GoVars.cmake b/cmake/modules/GoVars.cmake
index 4579e70..ec6f6b2 100644
--- a/cmake/modules/GoVars.cmake
+++ b/cmake/modules/GoVars.cmake
@@ -32,9 +32,10 @@
 endif()
 
 # We need a working shell. 
-set(shell $ENV{SHELL})
-if(shell STREQUAL "")
-set(shell "/bin/bash")
+if(DEFINED ENV{SHELL})
+  set(shell $ENV{SHELL})
+else()
+  set(shell "/bin/bash")
 endif()
 execute_process(COMMAND "${shell}" "-c" "echo foo" OUTPUT_VARIABLE echofoo)
 if(echofoo STREQUAL "")