diff --git a/CHANGELOG.md b/CHANGELOG.md
index a712d6d..68828a2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,9 @@
   This skips unnecessary network requests (thanks @hori-ryota)
 
 ## Fixed
+- #517: Fixed failure to install testImport from lock when no imports present
+  or when same dependency on both import and testImport
+- #440: Fixed panic in `glide tree` when walking the filesystem (thanks @abhin4v)
 - #529: --delete flag deleted and re-downloaded transitive dependencies
 - #535: Resolve vendor directory symlinks (thanks @Fugiman)
 
diff --git a/action/get.go b/action/get.go
index 0d5e004..696c50c 100644
--- a/action/get.go
+++ b/action/get.go
@@ -103,7 +103,10 @@
 	if err != nil {
 		msg.Die("Failed to generate config hash. Unable to generate lock file.")
 	}
-	lock := cfg.NewLockfile(confcopy.Imports, confcopy.DevImports, hash)
+	lock, err := cfg.NewLockfile(confcopy.Imports, confcopy.DevImports, hash)
+	if err != nil {
+		msg.Die("Failed to generate lock file: %s", err)
+	}
 	if err := lock.WriteFile(filepath.Join(base, gpath.LockFile)); err != nil {
 		msg.Die("Failed to write glide lock file: %s", err)
 	}
diff --git a/action/update.go b/action/update.go
index 91891f4..19ede20 100644
--- a/action/update.go
+++ b/action/update.go
@@ -71,7 +71,10 @@
 		if err != nil {
 			msg.Die("Failed to generate config hash. Unable to generate lock file.")
 		}
-		lock := cfg.NewLockfile(confcopy.Imports, confcopy.DevImports, hash)
+		lock, err := cfg.NewLockfile(confcopy.Imports, confcopy.DevImports, hash)
+		if err != nil {
+			msg.Die("Failed to generate lock file: %s", err)
+		}
 		wl := true
 		if gpath.HasLock(base) {
 			yml, err := ioutil.ReadFile(filepath.Join(base, gpath.LockFile))
diff --git a/cfg/lock.go b/cfg/lock.go
index 8a26e24..62d08ef 100644
--- a/cfg/lock.go
+++ b/cfg/lock.go
@@ -2,6 +2,7 @@
 
 import (
 	"crypto/sha256"
+	"fmt"
 	"io/ioutil"
 	"sort"
 	"strings"
@@ -40,6 +41,27 @@
 	for _, imp := range lf.Imports {
 		sort.Strings(imp.Subpackages)
 	}
+
+	// Ensure elements on testImport don't already exist on import.
+	var newDI Locks
+	var found bool
+	for _, imp := range lf.DevImports {
+		found = false
+		for i := 0; i < len(lf.Imports); i++ {
+			if lf.Imports[i].Name == imp.Name {
+				found = true
+				if lf.Imports[i].Version != imp.Version {
+					return lf, fmt.Errorf("Generating lock YAML produced conflicting versions of %s. import (%s), testImport (%s)", imp.Name, lf.Imports[i].Version, imp.Version)
+				}
+			}
+		}
+
+		if !found {
+			newDI = append(newDI, imp)
+		}
+	}
+	lf.DevImports = newDI
+
 	for _, imp := range lf.DevImports {
 		sort.Strings(imp.Subpackages)
 	}
@@ -169,7 +191,7 @@
 }
 
 // NewLockfile is used to create an instance of Lockfile.
-func NewLockfile(ds, tds Dependencies, hash string) *Lockfile {
+func NewLockfile(ds, tds Dependencies, hash string) (*Lockfile, error) {
 	lf := &Lockfile{
 		Hash:       hash,
 		Updated:    time.Now(),
@@ -183,13 +205,26 @@
 
 	sort.Sort(lf.Imports)
 
+	var found bool
 	for i := 0; i < len(tds); i++ {
-		lf.DevImports[i] = LockFromDependency(tds[i])
+		found = false
+		for ii := 0; ii < len(ds); ii++ {
+			if ds[ii].Name == tds[i].Name {
+				found = true
+				if ds[ii].Reference != tds[i].Reference {
+					return &Lockfile{}, fmt.Errorf("Generating lock produced conflicting versions of %s. import (%s), testImport (%s)", tds[i].Name, ds[ii].Reference, tds[i].Reference)
+				}
+				break
+			}
+		}
+		if !found {
+			lf.DevImports[i] = LockFromDependency(tds[i])
+		}
 	}
 
 	sort.Sort(lf.DevImports)
 
-	return lf
+	return lf, nil
 }
 
 // LockfileFromMap takes a map of dependencies and generates a lock Lockfile instance.
diff --git a/repo/installer.go b/repo/installer.go
index 433dca2..661106e 100644
--- a/repo/installer.go
+++ b/repo/installer.go
@@ -85,8 +85,8 @@
 
 	newConf.DeDupe()
 
-	if len(newConf.Imports) == 0 {
-		msg.Info("No dependencies found. Nothing installed.\n")
+	if len(newConf.Imports) == 0 && len(newConf.DevImports) == 0 {
+		msg.Info("No dependencies found. Nothing installed.")
 		return newConf, nil
 	}
 
diff --git a/repo/set_reference.go b/repo/set_reference.go
index 26c2e75..d9899ec 100644
--- a/repo/set_reference.go
+++ b/repo/set_reference.go
@@ -3,8 +3,10 @@
 import (
 	"sync"
 
+	"github.com/Masterminds/glide/cache"
 	"github.com/Masterminds/glide/cfg"
 	"github.com/Masterminds/glide/msg"
+	"github.com/codegangsta/cli"
 )
 
 // SetReference is a command to set the VCS reference (commit id, tag, etc) for
@@ -19,15 +21,40 @@
 	done := make(chan struct{}, concurrentWorkers)
 	in := make(chan *cfg.Dependency, concurrentWorkers)
 	var wg sync.WaitGroup
+	var lock sync.Mutex
+	var returnErr error
 
 	for i := 0; i < concurrentWorkers; i++ {
 		go func(ch <-chan *cfg.Dependency) {
 			for {
 				select {
 				case dep := <-ch:
+
+					var loc string
+					if dep.Repository != "" {
+						loc = dep.Repository
+					} else {
+						loc = "https://" + dep.Name
+					}
+					key, err := cache.Key(loc)
+					if err != nil {
+						msg.Die(err.Error())
+					}
+					cache.Lock(key)
 					if err := VcsVersion(dep); err != nil {
 						msg.Err("Failed to set version on %s to %s: %s\n", dep.Name, dep.Reference, err)
+
+						// Capture the error while making sure the concurrent
+						// operations don't step on each other.
+						lock.Lock()
+						if returnErr == nil {
+							returnErr = err
+						} else {
+							returnErr = cli.NewMultiError(returnErr, err)
+						}
+						lock.Unlock()
 					}
+					cache.Unlock(key)
 					wg.Done()
 				case <-done:
 					return
@@ -60,5 +87,5 @@
 	// close(done)
 	// close(in)
 
-	return nil
+	return returnErr
 }
diff --git a/tree/tree.go b/tree/tree.go
index 0dc3df7..e16478c 100644
--- a/tree/tree.go
+++ b/tree/tree.go
@@ -45,6 +45,10 @@
 func walkDeps(b *util.BuildCtxt, base, myName string) []string {
 	externalDeps := []string{}
 	filepath.Walk(base, func(path string, fi os.FileInfo, err error) error {
+		if err != nil {
+			return err
+		}
+
 		if !dependency.IsSrcDir(fi) {
 			if fi.IsDir() {
 				return filepath.SkipDir