diff --git a/pkg/metrics/metrics.go b/pkg/metrics/metrics.go
index 952c4ac..56be83d 100644
--- a/pkg/metrics/metrics.go
+++ b/pkg/metrics/metrics.go
@@ -133,17 +133,26 @@ func Register() {
 	)
 }
 
-func RegisterCollector(collector prometheus.Collector) {
+// RegisterCollector registers a collector and returns the collector to record
+// observations on. If an equal collector is already registered, that one is returned
+// instead; observations on the given collector would otherwise never be scraped.
+// Registration errors are logged, as they would leave the collector silently absent
+// from the metrics endpoint.
+func RegisterCollector[T prometheus.Collector](collector T) T {
 	err := prometheus.DefaultRegisterer.Register(collector)
 	if err == nil {
-		return
+		return collector
 	}
 
-	if _, ok := errors.AsType[prometheus.AlreadyRegisteredError](err); ok {
-		return
+	if alreadyRegistered, ok := errors.AsType[prometheus.AlreadyRegisteredError](err); ok {
+		if existing, ok := alreadyRegistered.ExistingCollector.(T); ok {
+			return existing
+		}
+		return collector
 	}
 
 	log.Warnf("metrics: registering collector: %+v", err)
+	return collector
 }
 
 func ObserveRedisLatency(operation string, fun func() error) error {
diff --git a/pkg/metrics/metrics_test.go b/pkg/metrics/metrics_test.go
new file mode 100644
index 0000000..ea850ff
--- /dev/null
+++ b/pkg/metrics/metrics_test.go
@@ -0,0 +1,28 @@
+package metrics_test
+
+import (
+	"testing"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/stretchr/testify/assert"
+
+	"github.com/nais/wonderwall/pkg/metrics"
+)
+
+func TestRegisterCollector(t *testing.T) {
+	newCounter := func() *prometheus.CounterVec {
+		return prometheus.NewCounterVec(prometheus.CounterOpts{
+			Name: "wonderwall_test_register_collector_total",
+			Help: "counter used to assert registration behaviour",
+		}, []string{"label"})
+	}
+
+	first := newCounter()
+	assert.Same(t, first, metrics.RegisterCollector(first), "the first registration is used as-is")
+
+	// an equal collector is already registered, so observations on the second one would
+	// never be scraped; the registered one must be returned instead
+	second := newCounter()
+	assert.Same(t, first, metrics.RegisterCollector(second))
+	assert.NotSame(t, second, metrics.RegisterCollector(second))
+}
diff --git a/pkg/middleware/prometheus.go b/pkg/middleware/prometheus.go
index 1ba2c4f..a812e14 100644
--- a/pkg/middleware/prometheus.go
+++ b/pkg/middleware/prometheus.go
@@ -56,8 +56,8 @@ func Prometheus(provider string, buckets ...float64) *PrometheusMiddleware {
 		[]string{"code", "method", "path", "host"},
 	)
 
-	metrics.RegisterCollector(m.reqs)
-	metrics.RegisterCollector(m.latency)
+	m.reqs = metrics.RegisterCollector(m.reqs)
+	m.latency = metrics.RegisterCollector(m.latency)
 
 	return &m
 }