diff --git a/themes/base.theme.bash b/themes/base.theme.bash
index 430fb60d..e172dd0c 100644
--- a/themes/base.theme.bash
+++ b/themes/base.theme.bash
@@ -79,15 +79,20 @@ RBENV_THEME_PROMPT_SUFFIX='|'
 RBFU_THEME_PROMPT_PREFIX=' |'
 RBFU_THEME_PROMPT_SUFFIX='|'
 
+GIT_EXE=`which git 2> /dev/null || true`
+P4_EXE=`which p4 2> /dev/null || true`
+HG_EXE=`which hg  2> /dev/null || true`
+SVN_EXE=`which svn  2> /dev/null || true`
+
 function scm {
   if [[ "$SCM_CHECK" = false ]]; then SCM=$SCM_NONE
-  elif [[ -f .git/HEAD ]] && which git &> /dev/null; then SCM=$SCM_GIT
-  elif which git &> /dev/null && [[ -n "$(git rev-parse --is-inside-work-tree 2> /dev/null)" ]]; then SCM=$SCM_GIT
-  elif which p4 &> /dev/null && [[ -n "$(p4 set P4CLIENT 2> /dev/null)" ]]; then SCM=$SCM_P4
-  elif [[ -d .hg ]] && which hg &> /dev/null; then SCM=$SCM_HG
-  elif which hg &> /dev/null && [[ -n "$(hg root 2> /dev/null)" ]]; then SCM=$SCM_HG
-  elif [[ -d .svn ]] && which svn &> /dev/null; then SCM=$SCM_SVN
-  elif which svn &> /dev/null && [[ -n "$(svn info --show-item wc-root 2>/dev/null)" ]]; then SCM=$SCM_SVN
+  elif [[ -f .git/HEAD ]] && [[ -x "$GIT_EXE" ]]; then SCM=$SCM_GIT
+  elif [[ -x "$GIT_EXE" ]] && [[ -n "$(git rev-parse --is-inside-work-tree 2> /dev/null)" ]]; then SCM=$SCM_GIT
+  elif [[ -x "$P4_EXE" ]] && [[ -n "$(p4 set P4CLIENT 2> /dev/null)" ]]; then SCM=$SCM_P4
+  elif [[ -d .hg ]] && [[ -x "$HG_EXE" ]]; then SCM=$SCM_HG
+  elif [[ -x "$HG_EXE" ]] && [[ -n "$(hg root 2> /dev/null)" ]]; then SCM=$SCM_HG
+  elif [[ -d .svn ]] && [[ -x "$SVN_EXE" ]]; then SCM=$SCM_SVN
+  elif [[ -x "$SVN_EXE" ]] && [[ -n "$(svn info --show-item wc-root 2>/dev/null)" ]]; then SCM=$SCM_SVN
   else SCM=$SCM_NONE
   fi
 }
@@ -503,4 +508,4 @@ function safe_append_prompt_command {
 function _save-and-reload-history() {
   local autosave=${1:-0}
   [[ $autosave -eq 1 ]] && history -a && history -c && history -r
-}
\ No newline at end of file
+}