diff --git a/daemon/config/config.go b/daemon/config/config.go
index 63a5fd3643..5c103ec4aa 100644
--- a/daemon/config/config.go
+++ b/daemon/config/config.go
@@ -276,7 +276,7 @@ func MergeDaemonConfigurations(flagsConfig *Config, flags *pflag.FlagSet, config
 	}
 
 	if err := Validate(fileConfig); err != nil {
-		return nil, fmt.Errorf("file configuration validation failed (%v)", err)
+		return nil, fmt.Errorf("configuration validation from file failed (%v)", err)
 	}
 
 	// merge flags configuration on top of the file configuration
@@ -287,7 +287,7 @@ func MergeDaemonConfigurations(flagsConfig *Config, flags *pflag.FlagSet, config
 	// We need to validate again once both fileConfig and flagsConfig
 	// have been merged
 	if err := Validate(fileConfig); err != nil {
-		return nil, fmt.Errorf("file configuration validation failed (%v)", err)
+		return nil, fmt.Errorf("merged configuration validation from file and command line flags failed (%v)", err)
 	}
 
 	return fileConfig, nil
@@ -459,14 +459,12 @@ func Validate(config *Config) error {
 			return err
 		}
 	}
-
 	// validate MaxConcurrentDownloads
-	if config.IsValueSet("max-concurrent-downloads") && config.MaxConcurrentDownloads != nil && *config.MaxConcurrentDownloads < 0 {
+	if config.MaxConcurrentDownloads != nil && *config.MaxConcurrentDownloads < 0 {
 		return fmt.Errorf("invalid max concurrent downloads: %d", *config.MaxConcurrentDownloads)
 	}
-
 	// validate MaxConcurrentUploads
-	if config.IsValueSet("max-concurrent-uploads") && config.MaxConcurrentUploads != nil && *config.MaxConcurrentUploads < 0 {
+	if config.MaxConcurrentUploads != nil && *config.MaxConcurrentUploads < 0 {
 		return fmt.Errorf("invalid max concurrent uploads: %d", *config.MaxConcurrentUploads)
 	}
 
diff --git a/daemon/config/config_test.go b/daemon/config/config_test.go
index 5bddac650c..7508c213c4 100644
--- a/daemon/config/config_test.go
+++ b/daemon/config/config_test.go
@@ -103,6 +103,38 @@ func TestDaemonConfigurationMergeConflicts(t *testing.T) {
 	}
 }
 
+func TestDaemonConfigurationMergeConcurrent(t *testing.T) {
+	f, err := ioutil.TempFile("", "docker-config-")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	configFile := f.Name()
+	f.Write([]byte(`{"max-concurrent-downloads": 1}`))
+	f.Close()
+
+	_, err = MergeDaemonConfigurations(&Config{}, nil, configFile)
+	if err != nil {
+		t.Fatal("expected error, got nil")
+	}
+}
+
+func TestDaemonConfigurationMergeConcurrentError(t *testing.T) {
+	f, err := ioutil.TempFile("", "docker-config-")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	configFile := f.Name()
+	f.Write([]byte(`{"max-concurrent-downloads": -1}`))
+	f.Close()
+
+	_, err = MergeDaemonConfigurations(&Config{}, nil, configFile)
+	if err == nil {
+		t.Fatalf("expected no error, got error %v", err)
+	}
+}
+
 func TestDaemonConfigurationMergeConflictsWithInnerStructs(t *testing.T) {
 	f, err := ioutil.TempFile("", "docker-config-")
 	if err != nil {
@@ -240,6 +272,7 @@ func TestValidateConfigurationErrors(t *testing.T) {
 }
 
 func TestValidateConfiguration(t *testing.T) {
+	minusNumber := 4
 	testCases := []struct {
 		config *Config
 	}{
@@ -264,6 +297,28 @@ func TestValidateConfiguration(t *testing.T) {
 				},
 			},
 		},
+		{
+			config: &Config{
+				CommonConfig: CommonConfig{
+					MaxConcurrentDownloads: &minusNumber,
+					// This is weird...
+					ValuesSet: map[string]interface{}{
+						"max-concurrent-downloads": -1,
+					},
+				},
+			},
+		},
+		{
+			config: &Config{
+				CommonConfig: CommonConfig{
+					MaxConcurrentUploads: &minusNumber,
+					// This is weird...
+					ValuesSet: map[string]interface{}{
+						"max-concurrent-uploads": -1,
+					},
+				},
+			},
+		},
 	}
 	for _, tc := range testCases {
 		err := Validate(tc.config)