diff --git a/commands/command_unlock.go b/commands/command_unlock.go
index 95dc1822..b32d511d 100644
--- a/commands/command_unlock.go
+++ b/commands/command_unlock.go
@@ -4,6 +4,8 @@ import (
 	"encoding/json"
 	"os"
 
+	"github.com/git-lfs/git-lfs/git"
+	"github.com/git-lfs/git-lfs/locking"
 	"github.com/spf13/cobra"
 )
 
@@ -31,11 +33,16 @@ func unlockCommand(cmd *cobra.Command, args []string) {
 			Exit("Unable to determine path: %v", err.Error())
 		}
 
+		unlockCheckFileStatus(path)
+
 		err = lockClient.UnlockFile(path, unlockCmdFlags.Force)
 		if err != nil {
 			Exit("Unable to unlock: %v", err.Error())
 		}
 	} else if unlockCmdFlags.Id != "" {
+
+		unlockCheckFileStatusById(unlockCmdFlags.Id, lockClient)
+
 		err := lockClient.UnlockFileById(unlockCmdFlags.Id, unlockCmdFlags.Force)
 		if err != nil {
 			Exit("Unable to unlock %v: %v", unlockCmdFlags.Id, err.Error())
@@ -55,6 +62,41 @@ func unlockCommand(cmd *cobra.Command, args []string) {
 	Print("'%s' was unlocked", args[0])
 }
 
+func unlockCheckFileStatus(path string) {
+	modified, err := git.IsFileModified(path)
+
+	if err != nil {
+		Exit(err.Error())
+	}
+
+	if modified {
+		if unlockCmdFlags.Force {
+			// Only a warning
+			Error("Warning: unlocking with uncommitted changes because --force")
+		} else {
+			Exit("Cannot unlock file with uncommitted changes")
+		}
+
+	}
+}
+
+func unlockCheckFileStatusById(id string, lockClient *locking.Client) {
+	// Get the path so we can check the status
+	filter := map[string]string{"id": id}
+	// try local cache first
+	locks, _ := lockClient.SearchLocks(filter, 0, true)
+	if len(locks) == 0 {
+		// Fall back on calling server
+		locks, _ = lockClient.SearchLocks(filter, 0, false)
+	}
+
+	if len(locks) > 0 {
+		unlockCheckFileStatus(locks[0].Path)
+	}
+
+	// Don't block if we can't determine the path, may be cleaning up old data
+}
+
 func init() {
 	if !isCommandEnabled(cfg, "locks") {
 		return
diff --git a/git/git.go b/git/git.go
index 335a3bae..137f4814 100644
--- a/git/git.go
+++ b/git/git.go
@@ -1092,3 +1092,43 @@ func GetFilesChanged(from, to string) ([]string, error) {
 
 	return files, err
 }
+
+// IsFileModified returns whether the filepath specified is modified according
+// to `git status`. A file is modified if it has uncommitted changes in the
+// working copy or the index. This includes being untracked.
+func IsFileModified(filepath string) (bool, error) {
+
+	args := []string{
+		"-c", "core.quotepath=false", // handle special chars in filenames
+		"status",
+		"--porcelain",
+		"--", // separator in case filename ambiguous
+		filepath,
+	}
+	cmd := subprocess.ExecCommand("git", args...)
+	outp, err := cmd.StdoutPipe()
+	if err != nil {
+		return false, fmt.Errorf("Failed to call git status: %v", err)
+	}
+	if err := cmd.Start(); err != nil {
+		return false, fmt.Errorf("Failed to start git status: %v", err)
+	}
+	scanner := bufio.NewScanner(outp)
+	for scanner.Scan() {
+		line := scanner.Text()
+		// Porcelain format is "<I><W> <filename>"
+		// Where <I> = index status, <W> = working copy status
+		if len(line) > 3 {
+			// Double-check even though should be only match
+			if strings.TrimSpace(line[3:]) == filepath {
+				return true, nil
+			}
+		}
+
+	}
+	if err := cmd.Wait(); err != nil {
+		return false, fmt.Errorf("Git status failed: %v", err)
+	}
+
+	return false, nil
+}
diff --git a/test/test-unlock.sh b/test/test-unlock.sh
index d7418aa5..3a22ba3c 100755
--- a/test/test-unlock.sh
+++ b/test/test-unlock.sh
@@ -72,3 +72,52 @@ begin_test "unlocking a lock without sufficient info"
   assert_server_lock "$reponame" "$id"
 )
 end_test
+
+begin_test "unlocking a lock while uncommitted"
+(
+  set -e
+
+  reponame="unlock_modified"
+  setup_remote_repo_with_file "$reponame" "f.dat"
+
+  GITLFSLOCKSENABLED=1 git lfs lock "f.dat" | tee lock.log
+
+  id=$(grep -oh "\((.*)\)" lock.log | tr -d "()")
+  assert_server_lock "$reponame" "$id"
+
+  echo "\nSomething" >> f.dat
+
+  GITLFSLOCKSENABLED=1 git lfs unlock "f.dat" 2>&1 | tee unlock.log
+  [ ${PIPESTATUS[0]} -ne "0" ]
+
+  grep "Cannot unlock file with uncommitted changes" unlock.log
+
+  assert_server_lock "$reponame" "$id"
+
+  # should allow after discard
+  git checkout f.dat
+  GITLFSLOCKSENABLED=1 git lfs unlock "f.dat" 2>&1 | tee unlock.log
+  refute_server_lock "$reponame" "$id"
+)
+end_test
+
+begin_test "unlocking a lock while uncommitted with --force"
+(
+  set -e
+
+  reponame="unlock_modified_force"
+  setup_remote_repo_with_file "$reponame" "g.dat"
+
+  GITLFSLOCKSENABLED=1 git lfs lock "g.dat" | tee lock.log
+
+  id=$(grep -oh "\((.*)\)" lock.log | tr -d "()")
+  assert_server_lock "$reponame" "$id"
+
+  echo "\nSomething" >> g.dat
+
+  # should allow with --force
+  GITLFSLOCKSENABLED=1 git lfs unlock --force "g.dat" 2>&1 | tee unlock.log
+  grep "Warning: unlocking with uncommitted changes" unlock.log
+  refute_server_lock "$reponame" "$id"
+)
+end_test