diff --git a/lib/spack/spack/repo.py b/lib/spack/spack/repo.py
index b103ac1caf..61f5e1d28c 100644
--- a/lib/spack/spack/repo.py
+++ b/lib/spack/spack/repo.py
@@ -918,8 +918,12 @@ def _read_config(self):
     @autospec
     def get(self, spec):
         """Returns the package associated with the supplied spec."""
-        if not self.exists(spec.name):
-            raise UnknownPackageError(spec.name)
+        # NOTE: we only check whether the package is None here, not whether it
+        # actually exists, because we have to load it anyway, and that ends up
+        # checking for existence. We avoid constructing FastPackageChecker,
+        # which will stat all packages.
+        if spec.name is None:
+            raise UnknownPackageError(None, self)
 
         if spec.namespace and spec.namespace != self.namespace:
             raise UnknownPackageError(spec.name, self.namespace)
@@ -1064,7 +1068,16 @@ def all_package_classes(self):
 
     def exists(self, pkg_name):
         """Whether a package with the supplied name exists."""
-        return pkg_name in self._pkg_checker
+        if pkg_name is None:
+            return False
+
+        # if the FastPackageChecker is already constructed, use it
+        if self._fast_package_checker:
+            return pkg_name in self._pkg_checker
+
+        # if not, check for the package.py file
+        path = self.filename_for_package_name(pkg_name)
+        return os.path.exists(path)
 
     def last_mtime(self):
         """Time a package file in this repo was last updated."""
@@ -1331,7 +1344,7 @@ def __init__(self, name, repo=None):
         long_msg = None
         if name:
             if repo:
-                msg = "Package '{0}' not found in repository '{1}'"
+                msg = "Package '{0}' not found in repository '{1.root}'"
                 msg = msg.format(name, repo)
             else:
                 msg = "Package '{0}' not found.".format(name)
diff --git a/lib/spack/spack/spec.py b/lib/spack/spack/spec.py
index aceceda081..609b20e238 100644
--- a/lib/spack/spack/spec.py
+++ b/lib/spack/spack/spec.py
@@ -3193,25 +3193,23 @@ def satisfies(self, other, deps=True, strict=False, strict_deps=False):
         if other.concrete:
             return self.concrete and self.dag_hash() == other.dag_hash()
 
-        # A concrete provider can satisfy a virtual dependency.
-        if not self.virtual and other.virtual:
-            try:
-                pkg = spack.repo.get(self.fullname)
-            except spack.repo.UnknownEntityError:
-                # If we can't get package info on this spec, don't treat
-                # it as a provider of this vdep.
-                return False
-
-            if pkg.provides(other.name):
-                for provided, when_specs in pkg.provided.items():
-                    if any(self.satisfies(when_spec, deps=False, strict=strict)
-                           for when_spec in when_specs):
-                        if provided.satisfies(other):
-                            return True
-            return False
-
-        # Otherwise, first thing we care about is whether the name matches
+        # If the names are different, we need to consider virtuals
         if self.name != other.name and self.name and other.name:
+            # A concrete provider can satisfy a virtual dependency.
+            if not self.virtual and other.virtual:
+                try:
+                    pkg = spack.repo.get(self.fullname)
+                except spack.repo.UnknownEntityError:
+                    # If we can't get package info on this spec, don't treat
+                    # it as a provider of this vdep.
+                    return False
+
+                if pkg.provides(other.name):
+                    for provided, when_specs in pkg.provided.items():
+                        if any(self.satisfies(when, deps=False, strict=strict)
+                               for when in when_specs):
+                            if provided.satisfies(other):
+                                return True
             return False
 
         # namespaces either match, or other doesn't require one.
@@ -4639,7 +4637,8 @@ def spec(self, name):
                     break
 
             elif self.accept(HASH):
-                # Get spec by hash and confirm it matches what we already have
+                # Get spec by hash and confirm it matches any constraints we
+                # already read in
                 hash_spec = self.spec_by_hash()
                 if hash_spec.satisfies(spec):
                     spec._dup(hash_spec)
diff --git a/lib/spack/spack/test/cmd/pkg.py b/lib/spack/spack/test/cmd/pkg.py
index 4f4293d004..f9311b14bc 100644
--- a/lib/spack/spack/test/cmd/pkg.py
+++ b/lib/spack/spack/test/cmd/pkg.py
@@ -129,7 +129,8 @@ def test_pkg_add(mock_pkg_git_repo):
         finally:
             shutil.rmtree('pkg-e')
             # Removing a package mid-run disrupts Spack's caching
-            spack.repo.path.repos[0]._fast_package_checker.invalidate()
+            if spack.repo.path.repos[0]._fast_package_checker:
+                spack.repo.path.repos[0]._fast_package_checker.invalidate()
 
     with pytest.raises(spack.main.SpackCommandError):
         pkg('add', 'does-not-exist')