diff --git a/plugins/themes/themes.plugin.zsh b/plugins/themes/themes.plugin.zsh
index 9c1b47fcf..eb3ae6b0e 100644
--- a/plugins/themes/themes.plugin.zsh
+++ b/plugins/themes/themes.plugin.zsh
@@ -1,3 +1,8 @@
+# Set to true to enable debugging output for theme functions
+# Note that this can cause unstable behavior, especially with these themes:
+# agnoster dstufft
+ZSH_THEME_DEBUG=${ZSH_THEME_DEBUG:-false}
+
 # Load a theme
 # 
 # Usage:
@@ -23,8 +28,8 @@ function theme() {
     found=false
     for theme_dir ($ZSH_CUSTOM $ZSH_CUSTOM/themes $ZSH/themes); do
       if [[ -f "$theme_dir/$name.zsh-theme" ]]; then
-        source "$theme_dir/$name.zsh-theme"
         found=true
+        _omz_load_theme_from_file $name "$theme_dir/$name.zsh-theme"
         break
       fi
     done
@@ -35,10 +40,169 @@ function theme() {
   fi
 }
 
+# Variables to track hook functions installed by themes
+_OMZ_THEME_CHPWD_FUNCTIONS=()
+_OMZ_THEME_PRECMD_FUNCTIONS=()
+_OMZ_THEME_PREEXEC_FUNCTIONS=()
+
+# Implementation of loading a theme
+# Most of the code in here is for tracking hooks and debugging support
+function _omz_load_theme_from_file() {
+  local name=$1 file=$2 params_before exclude_params
+  local -A values_before
+
+  # Reset so theme is loaded into a clean slate
+  _omz_reset_theme
+
+  # Set up tracking and debugging
+  local chpwd_fcns_0 precmd_fcns_0 preexec_fcns_0 chpwd_0 precmd_0 preexec_0
+  local params_after params_added param ignore_params
+  chpwd_0=$(which chpwd)
+  precmd_0=$(which precmd)
+  preexec_0=$(which preexec)
+  chpwd_fcns_0=($chpwd_functions)
+  precmd_fcns_0=($precmd_functions)
+  preexec_fcns_0=($preexec_functions)
+  if [[ $ZSH_THEME_DEBUG == true ]]; then
+    params_before=($(set +))
+  fi
+  for param ($params_before); do
+    values_before[$param]=${(P)param}
+  done
+
+  # Actually load the theme
+  source $file
+
+  # Debugging stuff
+  if [[ $ZSH_THEME_DEBUG == true ]]; then
+    params_after=($(set +))
+    params_added=(${params_after:|params_before})
+    ignore_params=(LINENO RANDOM _ parameters prompt values_before modules \
+      params_added ignore_params params_before params_after params_changed \
+      SECONDS TTYIDLE)
+    params_before=(${params_before:|ignore_params})
+    local params_changed
+    params_changed=()
+    for param ($params_before); do
+      if [[ ${(P)param} != ${values_before[$param]} ]]; then
+        params_changed+=($param)
+      fi
+    done
+  fi
+
+  # Track changes to hooks
+  _OMZ_THEME_CHPWD_FUNCTIONS=(${chpwd_functions:|chpwd_fcns_0})
+  _OMZ_THEME_PRECMD_FUNCTIONS=(${precmd_functions:|precmd_fcns_0})
+  _OMZ_THEME_PREEXEC_FUNCTIONS=(${preexec_functions:|preexec_fcns_0})
+
+  # Post-loading debugging
+  if [[ $ZSH_THEME_DEBUG == true ]]; then
+    echo "Loaded theme $name from file $file"
+    if [[ -n $params_added ]]; then
+      printf '=== %s ===\n%s\n' "Theme added parameters:" ${(F)params_added}
+    fi
+    if [[ -n $params_changed ]]; then
+      printf '=== %s ===\n%s\n' "Theme changed parameters:" ${(F)params_changed}
+    fi
+    if [[ -n "$_OMZ_THEME_CHPWD_FUNCTIONS$_OMZ_THEME_PRECMD_FUNCTIONS$_OMZ_THEME_PREEXEC_FUNCTIONS" ]]; then
+      printf '=== %s ===\n' "Theme added hooks:"
+      if [[ -n $_OMZ_THEME_CHPWD_FUNCTIONS ]]; then
+        echo "Theme added chpwd hooks: $_OMZ_THEME_CHPWD_FUNCTIONS"
+      fi
+      if [[ -n $_OMZ_THEME_PRECMD_FUNCTIONS ]]; then
+        echo "Theme added precmd hooks: $_OMZ_THEME_PRECMD_FUNCTIONS"
+      fi
+      if [[ -n $_OMZ_THEME_PREEXEC_FUNCTIONS ]]; then
+        echo "Theme added preexec hooks: $_OMZ_THEME_PREEXEC_FUNCTIONS"
+      fi
+    fi
+    if [[ $(which chpwd) != $chpwd_0 ]]; then
+      echo "WARNING: Theme changed chpwd()"
+    fi
+    if [[ $(which preexec) != $preexec_0 ]]; then
+      echo "WARNING: Theme changed preexec()"
+    fi
+    if [[ $(which precmd) != $precmd_0 ]]; then
+      echo "WARNING: Theme changed precmd()"
+    fi
+  fi
+}
+
+# Resets all theme settings to their default state
+# (To the extent that we know what themes do, that is.)
+# This will reset all variables used by the core OMZ *_prompt_info functions.
+# It will also remove any hook functions installed by the current theme, if it
+# was loaded by the theme() function
+function _omz_reset_theme() {
+  PROMPT="%n@%m:%~%# "
+
+  # This assumes that all ZSH_THEME_<aspect>_* variables are owned by
+  # OMZ theming, and can be reset en masse
+  # All the commented-out variables are there to serve as a list of things
+  # that are used by theme support and could be given default values
+
+  # git_prompt_info variables
+  unset -m 'ZSH_THEME_GIT_PROMPT_*'
+  ZSH_THEME_GIT_PROMPT_PREFIX="git:("   # Prefix at the very beginning of the prompt, before the branch name
+  ZSH_THEME_GIT_PROMPT_SUFFIX=")"       # At the very end of the prompt
+  #ZSH_THEME_GIT_PROMPT_PREFIX=
+  #ZSH_THEME_GIT_PROMPT_SUFFIX=
+  #ZSH_THEME_GIT_COMMITS_AHEAD_PREFIX=
+  #ZSH_THEME_GIT_COMMITS_AHEAD_SUFFIX=
+  ZSH_THEME_GIT_PROMPT_DIRTY="*"              # Text to display if the branch is dirty
+  ZSH_THEME_GIT_PROMPT_CLEAN=""               # Text to display if the branch is clean
+  #ZSH_THEME_GIT_PROMPT_BEHIND_REMOTE=
+  #ZSH_THEME_GIT_PROMPT_AHEAD_REMOTE=
+  #ZSH_THEME_GIT_PROMPT_DIVERGED_REMOTE=
+  #ZSH_THEME_GIT_PROMPT_AHEAD=
+  #ZSH_THEME_GIT_PROMPT_BEHIND=
+  #ZSH_THEME_GIT_PROMPT_SHA_BEFORE=
+  #ZSH_THEME_GIT_PROMPT_SHA_AFTER=
+  #ZSH_THEME_GIT_PROMPT_ADDED=
+  #ZSH_THEME_GIT_PROMPT_MODIFIED=
+  #ZSH_THEME_GIT_PROMPT_RENAMED=
+  #ZSH_THEME_GIT_PROMPT_DELETED=
+  #ZSH_THEME_GIT_PROMPT_STASHED=
+  #ZSH_THEME_GIT_PROMPT_UNMERGED=
+  #ZSH_THEME_GIT_PROMPT_DIVERGED=
+  #ZSH_THEME_GIT_PROMPT_UNTRACKED=
+  # nvm_prompt_info variables
+  unset -m 'ZSH_THEME_NVM_PROMPT_*'
+  #ZSH_THEME_NVM_PROMPT_PREFIX=
+  #ZSH_THEME_NVM_PROMPT_SUFFIX=
+  # rvm_prompt_info variables
+  unset -m 'ZSH_THEME_RVM_PROMPT_*'
+  #ZSH_THEME_RVM_PROMPT_PREFIX=
+  #ZSH_THEME_RVM_PROMPT_SUFFIX=
+  #ZSH_THEME_RVM_PROMPT_OPTIONS=
+  # svn_prompt_info variables
+  unset -m 'ZSH_THEME_SVN_PROMPT_*'
+  #ZSH_THEME_SVN_PROMPT_CLEAN
+  #ZSH_THEME_SVN_PROMPT_DIRTY
+  #ZSH_THEME_SVN_PROMPT_PREFIX
+  #ZSH_THEME_SVN_PROMPT_SUFFIX
+
+  # Hook functions
+  if [[ -n $_OMZ_THEME_CHPWD_FUNCTIONS ]]; then
+    #echo Removing chpwd hooks: $_OMZ_THEME_CHPWD_FUNCTIONS
+    chpwd_functions=(${chpwd_functions:|_OMZ_THEME_CHPWD_FUNCTIONS})
+  fi
+  if [[ -n $_OMZ_THEME_PRECMD_FUNCTIONS ]]; then
+    #echo Removing precmd hooks: $_OMZ_THEME_PRECMD_FUNCTIONS
+    precmd_functions=(${precmd_functions:|_OMZ_THEME_PRECMD_FUNCTIONS})
+  fi
+  if [[ -n $_OMZ_THEME_PREEXEC_FUNCTIONS ]]; then
+    #echo Removing preexec hooks: $_OMZ_THEME_PREEXEC_FUNCTIONS
+    preexec_functions=(${preexec_functions:|_OMZ_THEME_PREEXEC_FUNCTIONS})
+  fi
+
+}
+
+
 # List available themes by name
 #
 # The list will always be in sorted order, so you can index in to it.
-function lstheme(){
+function lstheme() {
   local themes x theme_dir
   themes=()
   for theme_dir ($ZSH_CUSTOM $ZSH_CUSTOM/themes $ZSH/themes); do
@@ -52,4 +216,6 @@ function lstheme(){
 # List themes defined in a given dir
 function _omz_lstheme_dir() {
   ls $1 | grep '.zsh-theme$' | sed 's,\.zsh-theme$,,'
-}
\ No newline at end of file
+}
+
+