diff --git a/cache/stringcache/chained_grouped_cache.go b/cache/stringcache/chained_grouped_cache.go
index 36f6fce1b..d2deb27a1 100644
--- a/cache/stringcache/chained_grouped_cache.go
+++ b/cache/stringcache/chained_grouped_cache.go
@@ -56,10 +56,14 @@ type chainedGroupFactory struct {
 	cacheFactories []GroupFactory
 }
 
-func (c *chainedGroupFactory) AddEntry(entry string) {
+func (c *chainedGroupFactory) AddEntry(entry string) bool {
 	for _, factory := range c.cacheFactories {
-		factory.AddEntry(entry)
+		if factory.AddEntry(entry) {
+			return true
+		}
 	}
+
+	return false
 }
 
 func (c *chainedGroupFactory) Count() int {
diff --git a/cache/stringcache/chained_grouped_cache_test.go b/cache/stringcache/chained_grouped_cache_test.go
index 9a04e9175..b4539614e 100644
--- a/cache/stringcache/chained_grouped_cache_test.go
+++ b/cache/stringcache/chained_grouped_cache_test.go
@@ -44,12 +44,12 @@ var _ = Describe("Chained grouped cache", func() {
 			})
 
 			It("factory has 4 elements (both caches)", func() {
-				Expect(factory.Count()).Should(BeNumerically("==", 4))
+				Expect(factory.Count()).Should(BeNumerically("==", 2))
 			})
 
 			It("should have element count of 4", func() {
 				factory.Finish()
-				Expect(cache.ElementCount("group1")).Should(BeNumerically("==", 4))
+				Expect(cache.ElementCount("group1")).Should(BeNumerically("==", 2))
 			})
 
 			It("should find strings", func() {
@@ -80,8 +80,8 @@ var _ = Describe("Chained grouped cache", func() {
 			})
 
 			It("should contain 4 elements in 2 groups", func() {
-				Expect(cache.ElementCount("group1")).Should(BeNumerically("==", 4))
-				Expect(cache.ElementCount("group2")).Should(BeNumerically("==", 4))
+				Expect(cache.ElementCount("group1")).Should(BeNumerically("==", 2))
+				Expect(cache.ElementCount("group2")).Should(BeNumerically("==", 2))
 				Expect(cache.Contains("g1", []string{"group1", "group2"})).Should(ConsistOf("group1"))
 				Expect(cache.Contains("g2", []string{"group1", "group2"})).Should(ConsistOf("group2"))
 				Expect(cache.Contains("both", []string{"group1", "group2"})).Should(ConsistOf("group1", "group2"))
@@ -92,8 +92,8 @@ var _ = Describe("Chained grouped cache", func() {
 				factory.AddEntry("newString")
 				factory.Finish()
 
-				Expect(cache.ElementCount("group1")).Should(BeNumerically("==", 2))
-				Expect(cache.ElementCount("group2")).Should(BeNumerically("==", 4))
+				Expect(cache.ElementCount("group1")).Should(BeNumerically("==", 1))
+				Expect(cache.ElementCount("group2")).Should(BeNumerically("==", 2))
 				Expect(cache.Contains("g1", []string{"group1", "group2"})).Should(BeEmpty())
 				Expect(cache.Contains("newString", []string{"group1", "group2"})).Should(ConsistOf("group1"))
 				Expect(cache.Contains("g2", []string{"group1", "group2"})).Should(ConsistOf("group2"))
diff --git a/cache/stringcache/grouped_cache_interface.go b/cache/stringcache/grouped_cache_interface.go
index 779de81b9..53dec3c05 100644
--- a/cache/stringcache/grouped_cache_interface.go
+++ b/cache/stringcache/grouped_cache_interface.go
@@ -15,7 +15,7 @@ type GroupedStringCache interface {
 
 type GroupFactory interface {
 	// AddEntry adds a new string to the factory to be added later to the cache groups.
-	AddEntry(entry string)
+	AddEntry(entry string) bool
 
 	// Count returns amount of processed string in the factory
 	Count() int
diff --git a/cache/stringcache/in_memory_grouped_cache.go b/cache/stringcache/in_memory_grouped_cache.go
index 38d1acd7f..a087da397 100644
--- a/cache/stringcache/in_memory_grouped_cache.go
+++ b/cache/stringcache/in_memory_grouped_cache.go
@@ -68,8 +68,8 @@ type inMemoryGroupFactory struct {
 	finishFn func(stringCache)
 }
 
-func (c *inMemoryGroupFactory) AddEntry(entry string) {
-	c.factory.addEntry(entry)
+func (c *inMemoryGroupFactory) AddEntry(entry string) bool {
+	return c.factory.addEntry(entry)
 }
 
 func (c *inMemoryGroupFactory) Count() int {
diff --git a/cache/stringcache/in_memory_grouped_cache_test.go b/cache/stringcache/in_memory_grouped_cache_test.go
index bddb7d4b6..f239795e5 100644
--- a/cache/stringcache/in_memory_grouped_cache_test.go
+++ b/cache/stringcache/in_memory_grouped_cache_test.go
@@ -46,8 +46,8 @@ var _ = Describe("In-Memory grouped cache", func() {
 				cache = stringcache.NewInMemoryGroupedStringCache()
 				factory = cache.Refresh("group1")
 
-				factory.AddEntry("string1")
-				factory.AddEntry("string2")
+				Expect(factory.AddEntry("string1")).Should(BeTrue())
+				Expect(factory.AddEntry("string2")).Should(BeTrue())
 			})
 
 			It("cache should still have 0 element, since finish was not executed", func() {
@@ -69,28 +69,13 @@ var _ = Describe("In-Memory grouped cache", func() {
 				Expect(cache.Contains("string2", []string{"group1", "someOtherGroup"})).Should(ConsistOf("group1"))
 			})
 		})
-		When("String grouped cache is used", func() {
-			BeforeEach(func() {
-				cache = stringcache.NewInMemoryGroupedStringCache()
-				factory = cache.Refresh("group1")
-
-				factory.AddEntry("string1")
-				factory.AddEntry("/string2/")
-				factory.Finish()
-			})
-
-			It("should ignore regex", func() {
-				Expect(cache.ElementCount("group1")).Should(BeNumerically("==", 1))
-				Expect(cache.Contains("string1", []string{"group1"})).Should(ConsistOf("group1"))
-			})
-		})
 		When("Regex grouped cache is used", func() {
 			BeforeEach(func() {
 				cache = stringcache.NewInMemoryGroupedRegexCache()
 				factory = cache.Refresh("group1")
 
-				factory.AddEntry("string1")
-				factory.AddEntry("/string2/")
+				Expect(factory.AddEntry("string1")).Should(BeFalse())
+				Expect(factory.AddEntry("/string2/")).Should(BeTrue())
 				factory.Finish()
 			})
 
@@ -109,13 +94,13 @@ var _ = Describe("In-Memory grouped cache", func() {
 				cache = stringcache.NewInMemoryGroupedStringCache()
 				factory = cache.Refresh("group1")
 
-				factory.AddEntry("g1")
-				factory.AddEntry("both")
+				Expect(factory.AddEntry("g1")).Should(BeTrue())
+				Expect(factory.AddEntry("both")).Should(BeTrue())
 				factory.Finish()
 
 				factory = cache.Refresh("group2")
-				factory.AddEntry("g2")
-				factory.AddEntry("both")
+				Expect(factory.AddEntry("g2")).Should(BeTrue())
+				Expect(factory.AddEntry("both")).Should(BeTrue())
 				factory.Finish()
 			})
 
@@ -129,7 +114,7 @@ var _ = Describe("In-Memory grouped cache", func() {
 
 			It("Should replace group content on refresh", func() {
 				factory = cache.Refresh("group1")
-				factory.AddEntry("newString")
+				Expect(factory.AddEntry("newString")).Should(BeTrue())
 				factory.Finish()
 
 				Expect(cache.ElementCount("group1")).Should(BeNumerically("==", 1))
diff --git a/cache/stringcache/string_caches.go b/cache/stringcache/string_caches.go
index e8ad366ff..5bcd06edd 100644
--- a/cache/stringcache/string_caches.go
+++ b/cache/stringcache/string_caches.go
@@ -14,7 +14,7 @@ type stringCache interface {
 }
 
 type cacheFactory interface {
-	addEntry(entry string)
+	addEntry(entry string) bool
 	create() stringCache
 	count() int
 }
@@ -86,7 +86,7 @@ func (s *stringCacheFactory) insertString(entry string) {
 	ix := sort.SearchStrings(bucket, normalized)
 
 	if !(ix < len(bucket) && bucket[ix] == normalized) {
-		// extent internal bucket
+		// extend internal bucket
 		bucket = append(s.getBucket(entryLen), "")
 
 		// move elements to make place for the insertion
@@ -98,15 +98,22 @@ func (s *stringCacheFactory) insertString(entry string) {
 	}
 }
 
-func (s *stringCacheFactory) addEntry(entry string) {
-	// skip empty strings and regex
-	if len(entry) > 0 && !isRegex(entry) {
-		s.cnt++
-		s.insertString(entry)
+func (s *stringCacheFactory) addEntry(entry string) bool {
+	if len(entry) == 0 {
+		return true // invalid but handled
 	}
+
+	s.cnt++
+	s.insertString(entry)
+
+	return true
 }
 
 func (s *stringCacheFactory) create() stringCache {
+	if len(s.tmp) == 0 {
+		return nil
+	}
+
 	cache := make(stringMap, len(s.tmp))
 	for k, v := range s.tmp {
 		cache[k] = strings.Join(v, "")
@@ -117,10 +124,6 @@ func (s *stringCacheFactory) create() stringCache {
 	return cache
 }
 
-func isRegex(s string) bool {
-	return strings.HasPrefix(s, "/") && strings.HasSuffix(s, "/")
-}
-
 type regexCache []*regexp.Regexp
 
 func (cache regexCache) elementCount() int {
@@ -143,17 +146,24 @@ type regexCacheFactory struct {
 	cache regexCache
 }
 
-func (r *regexCacheFactory) addEntry(entry string) {
-	if isRegex(entry) {
-		entry = strings.TrimSpace(entry[1 : len(entry)-1])
-		compile, err := regexp.Compile(entry)
+func (r *regexCacheFactory) addEntry(entry string) bool {
+	if !strings.HasPrefix(entry, "/") || !strings.HasSuffix(entry, "/") {
+		return false
+	}
 
-		if err != nil {
-			log.Log().Warnf("invalid regex '%s'", entry)
-		} else {
-			r.cache = append(r.cache, compile)
-		}
+	// Trim slashes
+	entry = strings.TrimSpace(entry[1 : len(entry)-1])
+
+	compile, err := regexp.Compile(entry)
+	if err != nil {
+		log.Log().Warnf("invalid regex '%s'", entry)
+
+		return true // invalid but handled
 	}
+
+	r.cache = append(r.cache, compile)
+
+	return true
 }
 
 func (r *regexCacheFactory) count() int {
diff --git a/cache/stringcache/string_caches_benchmark_test.go b/cache/stringcache/string_caches_benchmark_test.go
index 60457ea92..8088824bc 100644
--- a/cache/stringcache/string_caches_benchmark_test.go
+++ b/cache/stringcache/string_caches_benchmark_test.go
@@ -14,7 +14,9 @@ func BenchmarkStringCache(b *testing.B) {
 		factory := newStringCacheFactory()
 
 		for _, s := range testdata {
-			factory.addEntry(s)
+			if !factory.addEntry(s) {
+				b.Fatalf("cache didn't insert value: %s", s)
+			}
 		}
 
 		factory.create()
diff --git a/cache/stringcache/string_caches_test.go b/cache/stringcache/string_caches_test.go
index 201e2c34c..a5d37bac2 100644
--- a/cache/stringcache/string_caches_test.go
+++ b/cache/stringcache/string_caches_test.go
@@ -10,15 +10,16 @@ var _ = Describe("Caches", func() {
 		cache   stringCache
 		factory cacheFactory
 	)
+
 	Describe("String StringCache", func() {
 		When("string StringCache was created", func() {
 			BeforeEach(func() {
 				factory = newStringCacheFactory()
-				factory.addEntry("google.com")
-				factory.addEntry("apple.com")
-				factory.addEntry("")
-				factory.addEntry("google.com")
-				factory.addEntry("APPLe.com")
+				Expect(factory.addEntry("google.com")).Should(BeTrue())
+				Expect(factory.addEntry("apple.com")).Should(BeTrue())
+				Expect(factory.addEntry("")).Should(BeTrue()) // invalid, but handled
+				Expect(factory.addEntry("google.com")).Should(BeTrue())
+				Expect(factory.addEntry("APPLe.com")).Should(BeTrue())
 
 				cache = factory.create()
 			})
@@ -29,13 +30,16 @@ var _ = Describe("Caches", func() {
 				Expect(cache.contains("www.google.com")).Should(BeFalse())
 				Expect(cache.contains("")).Should(BeFalse())
 			})
+
 			It("should match case-insensitive", func() {
 				Expect(cache.contains("aPPle.com")).Should(BeTrue())
 				Expect(cache.contains("google.COM")).Should(BeTrue())
 				Expect(cache.contains("www.google.com")).Should(BeFalse())
 				Expect(cache.contains("")).Should(BeFalse())
 			})
+
 			It("should return correct element count", func() {
+				Expect(factory.count()).Should(Equal(4))
 				Expect(cache.elementCount()).Should(Equal(2))
 			})
 		})
@@ -45,14 +49,15 @@ var _ = Describe("Caches", func() {
 		When("regex StringCache was created", func() {
 			BeforeEach(func() {
 				factory = newRegexCacheFactory()
-				factory.addEntry("/.*google.com/")
-				factory.addEntry("/^apple\\.(de|com)$/")
-				factory.addEntry("/amazon/")
-				// this is not a regex, will be ignored
-				factory.addEntry("/(wrongRegex/")
-				factory.addEntry("plaintext")
+				Expect(factory.addEntry("/.*google.com/")).Should(BeTrue())
+				Expect(factory.addEntry("/^apple\\.(de|com)$/")).Should(BeTrue())
+				Expect(factory.addEntry("/amazon/")).Should(BeTrue())
+				Expect(factory.addEntry("/(wrongRegex/")).Should(BeTrue()) // recognized as regex but ignored because invalid
+				Expect(factory.addEntry("plaintext")).Should(BeFalse())
+
 				cache = factory.create()
 			})
+
 			It("should match if one regex in StringCache matches string", func() {
 				Expect(cache.contains("google.com")).Should(BeTrue())
 				Expect(cache.contains("google.coma")).Should(BeTrue())
@@ -67,6 +72,7 @@ var _ = Describe("Caches", func() {
 				Expect(cache.contains("amazon.com")).Should(BeTrue())
 				Expect(cache.contains("myamazon.com")).Should(BeTrue())
 			})
+
 			It("should return correct element count", func() {
 				Expect(factory.count()).Should(Equal(3))
 				Expect(cache.elementCount()).Should(Equal(3))
diff --git a/lists/list_cache.go b/lists/list_cache.go
index f731b015b..94f149209 100644
--- a/lists/list_cache.go
+++ b/lists/list_cache.go
@@ -62,8 +62,8 @@ func NewListCache(ctx context.Context,
 ) (*ListCache, error) {
 	c := &ListCache{
 		groupedCache: stringcache.NewChainedGroupedCache(
-			stringcache.NewInMemoryGroupedStringCache(),
 			stringcache.NewInMemoryGroupedRegexCache(),
+			stringcache.NewInMemoryGroupedStringCache(),   // accepts all values, must be last
 		),
 
 		cfg:          cfg,
@@ -168,9 +168,11 @@ func (b *ListCache) createCacheForGroup(
 
 	producers.GoConsume(func(ctx context.Context, ch <-chan string) error {
 		for host := range ch {
-			hasEntries = true
-
-			groupFactory.AddEntry(host)
+			if groupFactory.AddEntry(host) {
+				hasEntries = true
+			} else {
+				logger().WithField("host", host).Warn("no list cache was able to use host")
+			}
 		}
 
 		return nil