diff --git a/cmd/prometheus/config.go b/cmd/prometheus/config.go
index 19858d1cd..35f8c0b8d 100644
--- a/cmd/prometheus/config.go
+++ b/cmd/prometheus/config.go
@@ -242,10 +242,12 @@ func parse(args []string) error {
 	if err := parsePrometheusURL(); err != nil {
 		return err
 	}
-
 	if err := parseInfluxdbURL(); err != nil {
 		return err
 	}
+	if err := validateAlertmanagerURL(); err != nil {
+		return err
+	}
 
 	cfg.remote.InfluxdbPassword = os.Getenv("INFLUXDB_PW")
 
@@ -266,7 +268,7 @@ func parsePrometheusURL() error {
 	}
 
 	if ok := govalidator.IsURL(cfg.prometheusURL); !ok {
-		return fmt.Errorf("Invalid Prometheus URL: %s", cfg.prometheusURL)
+		return fmt.Errorf("invalid Prometheus URL: %s", cfg.prometheusURL)
 	}
 
 	promURL, err := url.Parse(cfg.prometheusURL)
@@ -289,7 +291,7 @@ func parseInfluxdbURL() error {
 	}
 
 	if ok := govalidator.IsURL(cfg.influxdbURL); !ok {
-		return fmt.Errorf("Invalid InfluxDB URL: %s", cfg.influxdbURL)
+		return fmt.Errorf("invalid InfluxDB URL: %s", cfg.influxdbURL)
 	}
 
 	url, err := url.Parse(cfg.influxdbURL)
@@ -301,6 +303,23 @@ func parseInfluxdbURL() error {
 	return nil
 }
 
+func validateAlertmanagerURL() error {
+	if cfg.notifier.AlertmanagerURL == "" {
+		return nil
+	}
+	if ok := govalidator.IsURL(cfg.notifier.AlertmanagerURL); !ok {
+		return fmt.Errorf("invalid Alertmanager URL: %s", cfg.notifier.AlertmanagerURL)
+	}
+	url, err := url.Parse(cfg.notifier.AlertmanagerURL)
+	if err != nil {
+		return err
+	}
+	if url.Scheme == "" {
+		return fmt.Errorf("missing scheme in Alertmanager URL: %s", cfg.notifier.AlertmanagerURL)
+	}
+	return nil
+}
+
 var helpTmpl = `
 usage: prometheus [<args>]
 {{ range $cat, $flags := . }}{{ if ne $cat "." }} == {{ $cat | upper }} =={{ end }}
diff --git a/cmd/prometheus/config_test.go b/cmd/prometheus/config_test.go
index 4f5e8c112..a77eaf207 100644
--- a/cmd/prometheus/config_test.go
+++ b/cmd/prometheus/config_test.go
@@ -48,6 +48,18 @@ func TestParse(t *testing.T) {
 			input: []string{"-storage.remote.influxdb-url", "'https://some-url/'"},
 			valid: false,
 		},
+		{
+			input: []string{"-alertmanager.url", ""},
+			valid: true,
+		},
+		{
+			input: []string{"-alertmanager.url", "http://alertmanager.company.com"},
+			valid: true,
+		},
+		{
+			input: []string{"-alertmanager.url", "alertmanager.company.com"},
+			valid: false,
+		},
 	}
 
 	for i, test := range tests {
diff --git a/retrieval/targetmanager.go b/retrieval/targetmanager.go
index 6daa708fc..5ce1e98f8 100644
--- a/retrieval/targetmanager.go
+++ b/retrieval/targetmanager.go
@@ -15,6 +15,7 @@ package retrieval
 
 import (
 	"fmt"
+	"sort"
 	"strings"
 	"sync"
 	"time"
@@ -134,11 +135,11 @@ func (tm *TargetManager) reload() {
 }
 
 // Pools returns the targets currently being scraped bucketed by their job name.
-func (tm *TargetManager) Pools() map[string][]*Target {
+func (tm *TargetManager) Pools() map[string]Targets {
 	tm.mtx.RLock()
 	defer tm.mtx.RUnlock()
 
-	pools := map[string][]*Target{}
+	pools := map[string]Targets{}
 
 	// TODO(fabxc): this is just a hack to maintain compatibility for now.
 	for _, ps := range tm.targetSets {
@@ -151,6 +152,9 @@ func (tm *TargetManager) Pools() map[string][]*Target {
 
 		ps.scrapePool.mtx.RUnlock()
 	}
+	for _, targets := range pools {
+		sort.Sort(targets)
+	}
 	return pools
 }
 
@@ -274,28 +278,28 @@ func (ts *targetSet) runProviders(ctx context.Context, providers map[string]Targ
 		updates := make(chan []*config.TargetGroup)
 
 		go func(name string, prov TargetProvider) {
-			var initial []*config.TargetGroup
-
 			select {
 			case <-ctx.Done():
-				wg.Done()
-				return
-			case initial = <-updates:
+			case initial, ok := <-updates:
+				// Handle the case that a target provider exits and closes the channel
+				// before the context is done.
+				if !ok {
+					break
+				}
 				// First set of all targets the provider knows.
+				for _, tgroup := range initial {
+					targets, err := targetsFromGroup(tgroup, ts.config)
+					if err != nil {
+						log.With("target_group", tgroup).Errorf("Target update failed: %s", err)
+						continue
+					}
+					ts.tgroups[name+"/"+tgroup.Source] = targets
+				}
 			case <-time.After(5 * time.Second):
 				// Initial set didn't arrive. Act as if it was empty
 				// and wait for updates later on.
 			}
 
-			for _, tgroup := range initial {
-				targets, err := targetsFromGroup(tgroup, ts.config)
-				if err != nil {
-					log.With("target_group", tgroup).Errorf("Target update failed: %s", err)
-					continue
-				}
-				ts.tgroups[name+"/"+tgroup.Source] = targets
-			}
-
 			wg.Done()
 
 			// Start listening for further updates.
@@ -303,7 +307,12 @@ func (ts *targetSet) runProviders(ctx context.Context, providers map[string]Targ
 				select {
 				case <-ctx.Done():
 					return
-				case tgs := <-updates:
+				case tgs, ok := <-updates:
+					// Handle the case that a target provider exits and closes the channel
+					// before the context is done.
+					if !ok {
+						return
+					}
 					for _, tg := range tgs {
 						if err := ts.update(name, tg); err != nil {
 							log.With("target_group", tg).Errorf("Target update failed: %s", err)
diff --git a/web/web.go b/web/web.go
index bfcbdb639..8ce45cb26 100644
--- a/web/web.go
+++ b/web/web.go
@@ -92,7 +92,7 @@ type PrometheusStatus struct {
 
 	// A function that returns the current scrape targets pooled
 	// by their job name.
-	TargetPools func() map[string][]*retrieval.Target
+	TargetPools func() map[string]retrieval.Targets
 	// A function that returns all loaded rules.
 	Rules func() []rules.Rule