diff --git a/xonsh/environ.py b/xonsh/environ.py
index 8f66b2752..0fd12485f 100644
--- a/xonsh/environ.py
+++ b/xonsh/environ.py
@@ -816,17 +816,19 @@ def _yield_executables(directory, name):
 
 
 def locate_binary(name):
-    if os.path.isfile(name) and name != os.path.basename(name):
-        return name
-    directories = builtins.__xonsh_env__.get('PATH')
-    # Windows users expect to be able to execute files in the same directory
-    # without `./`
-    if ON_WINDOWS:
-        directories = [_get_cwd()] + list(directories)
-    try:
-        return next(chain.from_iterable(_yield_executables(directory, name) for
-                    directory in directories if os.path.isdir(directory)))
-    except StopIteration:
+    """Locates an executable on the file system."""
+    if os.path.isfile(name):
+        if ON_WINDOWS:
+            # Windows users expect to be able to execute files in the same
+            # directory without `./`
+            return os.path.abspath(os.path.relpath(name, _get_cwd()))
+        elif name != os.path.basename(name):
+            return name
+    cc = builtins.__xonsh_commands_cache__
+    if name in cc:
+        # can be lazy here since we know name is already available
+        return cc.lazyget(name)[0]
+    else:
         return None
 
 
diff --git a/xonsh/tools.py b/xonsh/tools.py
index 9509e5b63..77f4870fd 100644
--- a/xonsh/tools.py
+++ b/xonsh/tools.py
@@ -1476,17 +1476,22 @@ def expanduser_abs_path(inp):
     return os.path.abspath(os.path.expanduser(inp))
 
 
-class CommandsCache(abc.Set):
-    """A lazy cache representing the commands available on the file system."""
+class CommandsCache(abc.Mapping):
+    """A lazy cache representing the commands available on the file system.
+    The keys are the command names and the values a tuple of (loc, has_alias)
+    where loc is either a str pointing to the executable on the file system or
+    None (if no executable exists) and has_alias is a boolean flag for whether
+    the command has an alias.
+    """
 
     def __init__(self):
-        self._cmds_cache = frozenset()
+        self._cmds_cache = {}
         self._path_checksum = None
         self._alias_checksum = None
         self._path_mtime = -1
 
-    def __contains__(self, item):
-        return item in self.all_commands
+    def __contains__(self, key):
+        return key in self.all_commands
 
     def __iter__(self):
         return iter(self.all_commands)
@@ -1494,21 +1499,25 @@ class CommandsCache(abc.Set):
     def __len__(self):
         return len(self.all_commands)
 
+    def __getitem__(self, key):
+        return self.all_commands[key]
+
     @property
     def all_commands(self):
         paths = builtins.__xonsh_env__.get('PATH', [])
-        paths = frozenset(x for x in paths if os.path.isdir(x))
+        pathset = frozenset(x for x in paths if os.path.isdir(x))
         # did PATH change?
-        path_hash = hash(paths)
+        path_hash = hash(pathset)
         cache_valid = path_hash == self._path_checksum
         self._path_checksum = path_hash
         # did aliases change?
-        al_hash = hash(frozenset(builtins.aliases))
+        alss = builtins.aliases
+        al_hash = hash(frozenset(alss))
         cache_valid = cache_valid and al_hash == self._alias_checksum
         self._alias_checksum = al_hash
         # did the contents of any directory in PATH change?
         max_mtime = 0
-        for path in paths:
+        for path in pathset:
             mtime = os.stat(path).st_mtime
             if mtime > max_mtime:
                 max_mtime = mtime
@@ -1516,12 +1525,18 @@ class CommandsCache(abc.Set):
         self._path_mtime = max_mtime
         if cache_valid:
             return self._cmds_cache
-        allcmds = set()
-        for path in paths:
-            allcmds |= set(executables_in(path))
-            allcmds |= set(builtins.aliases)
-        self._cmds_cache = frozenset(allcmds)
-        return self._cmds_cache
+        allcmds = {}
+        for path in reversed(paths):
+            # iterate backwards so that entries at the front of PATH overwrite
+            # entries at the back.
+            for cmd in executables_in(path):
+                allcmds[cmd] = (os.path.join(path, cmd), cmd in alss)
+        only_alias = (None, True)
+        for cmd in alss:
+            if cmd not in allcmds:
+                allcmds[cmd] = only_alias
+        self._cmds_cache = allcmds
+        return allcmds
 
     def lazyin(self, value):
         """Checks if the value is in the current cache without the potential to
@@ -1544,6 +1559,10 @@ class CommandsCache(abc.Set):
         """
         return len(self._cmds_cache)
 
+    def lazyget(self, key, default=None):
+        """A lazy value getter."""
+        return self._cmd_cache.get(key, default)
+
 
 WINDOWS_DRIVE_MATCHER = LazyObject(lambda: re.compile(r'^\w:'),
                                    globals(), 'WINDOWS_DRIVE_MATCHER')