diff --git a/config/config.go b/config/config.go
index cd603e5f9a..2e941c426e 100644
--- a/config/config.go
+++ b/config/config.go
@@ -398,9 +398,28 @@ func (c *ScrapeConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
 	if c.BasicAuth != nil && (len(c.BearerToken) > 0 || len(c.BearerTokenFile) > 0) {
 		return fmt.Errorf("at most one of basic_auth, bearer_token & bearer_token_file must be configured")
 	}
+	// Check for users putting URLs in target groups.
+	if len(c.RelabelConfigs) == 0 {
+		for _, tg := range c.TargetGroups {
+			for _, t := range tg.Targets {
+				if err = CheckTargetAddress(t[model.AddressLabel]); err != nil {
+					return err
+				}
+			}
+		}
+	}
 	return checkOverflow(c.XXX, "scrape_config")
 }
 
+// CheckTargetAddress checks if target address is valid.
+func CheckTargetAddress(address model.LabelValue) error {
+	// For now check for a URL, we may want to expand this later.
+	if strings.Contains(string(address), "/") {
+		return fmt.Errorf("%q is not a valid hostname", address)
+	}
+	return nil
+}
+
 // BasicAuth contains basic HTTP authentication credentials.
 type BasicAuth struct {
 	Username string `yaml:"username"`
@@ -457,9 +476,6 @@ func (tg *TargetGroup) UnmarshalYAML(unmarshal func(interface{}) error) error {
 	}
 	tg.Targets = make([]model.LabelSet, 0, len(g.Targets))
 	for _, t := range g.Targets {
-		if strings.Contains(t, "/") {
-			return fmt.Errorf("%q is not a valid hostname", t)
-		}
 		tg.Targets = append(tg.Targets, model.LabelSet{
 			model.AddressLabel: model.LabelValue(t),
 		})
diff --git a/config/config_test.go b/config/config_test.go
index b1d19f27b9..853e65f029 100644
--- a/config/config_test.go
+++ b/config/config_test.go
@@ -335,6 +335,9 @@ var expectedErrors = []struct {
 	}, {
 		filename: "marathon_no_servers.bad.yml",
 		errMsg:   "Marathon SD config must contain at least one Marathon server",
+	}, {
+		filename: "url_in_targetgroup.bad.yml",
+		errMsg:   "\"http://bad\" is not a valid hostname",
 	},
 }
 
diff --git a/config/testdata/url_in_targetgroup.bad.yml b/config/testdata/url_in_targetgroup.bad.yml
new file mode 100644
index 0000000000..48a1845990
--- /dev/null
+++ b/config/testdata/url_in_targetgroup.bad.yml
@@ -0,0 +1,5 @@
+scrape_configs:
+- job_name: prometheus
+  target_groups:
+  - targets:
+    - http://bad
diff --git a/retrieval/targetmanager.go b/retrieval/targetmanager.go
index f301b9a1b2..fb98589133 100644
--- a/retrieval/targetmanager.go
+++ b/retrieval/targetmanager.go
@@ -496,6 +496,9 @@ func (tm *TargetManager) targetsFromGroup(tg *config.TargetGroup, cfg *config.Sc
 		if labels == nil {
 			continue
 		}
+		if err = config.CheckTargetAddress(labels[model.AddressLabel]); err != nil {
+			return nil, err
+		}
 
 		for ln := range labels {
 			// Meta labels are deleted after relabelling. Other internal labels propagate to
diff --git a/retrieval/targetmanager_test.go b/retrieval/targetmanager_test.go
index 3f605f7693..654083d3e9 100644
--- a/retrieval/targetmanager_test.go
+++ b/retrieval/targetmanager_test.go
@@ -278,6 +278,25 @@ func TestTargetManagerConfigUpdate(t *testing.T) {
 			},
 		},
 	}
+	// Test that targets without host:port addresses are dropped.
+	testJob3 := &config.ScrapeConfig{
+		JobName:        "test_job1",
+		ScrapeInterval: config.Duration(1 * time.Minute),
+		TargetGroups: []*config.TargetGroup{{
+			Targets: []model.LabelSet{
+				{model.AddressLabel: "example.net:80"},
+			},
+		}},
+		RelabelConfigs: []*config.RelabelConfig{
+			{
+				SourceLabels: model.LabelNames{model.AddressLabel},
+				Regex:        config.MustNewRegexp("(.*)"),
+				TargetLabel:  "__address__",
+				Replacement:  "http://$1",
+				Action:       config.RelabelReplace,
+			},
+		},
+	}
 
 	sequence := []struct {
 		scrapeConfigs []*config.ScrapeConfig
@@ -348,6 +367,9 @@ func TestTargetManagerConfigUpdate(t *testing.T) {
 						model.SchemeLabel: "", model.MetricsPathLabel: "", model.AddressLabel: "foo.com:1235"},
 				},
 			},
+		}, {
+			scrapeConfigs: []*config.ScrapeConfig{testJob3},
+			expected:      map[string][]model.LabelSet{},
 		},
 	}
 	conf := &config.Config{}