diff --git a/bin/brew b/bin/brew
index 4ac9473a77..7d36ff92d5 100755
--- a/bin/brew
+++ b/bin/brew
@@ -91,6 +91,9 @@ then
   for VAR in HOME SHELL PATH TERM LOGNAME USER CI TRAVIS \
              "${!HOMEBREW_@}" "${!TRAVIS_@}"
   do
+    # Skip if variable value is empty.
+    [[ -z "${!VAR}" ]] && continue
+
     FILTERED_ENV+=( "${VAR}=${!VAR}" )
   done