diff --git a/caddytest/integration/caddyfile_adapt_test.go b/caddytest/integration/caddyfile_adapt_test.go
index f6120aef..514a5064 100644
--- a/caddytest/integration/caddyfile_adapt_test.go
+++ b/caddytest/integration/caddyfile_adapt_test.go
@@ -362,4 +362,56 @@ func TestMatcherSyntax(t *testing.T) {
 		}
 	}
 }`)
-}
\ No newline at end of file
+}
+
+func TestNotBlockMerging(t *testing.T) {
+	caddytest.AssertAdapt(t, ` 
+	:80
+
+	@test {
+		not {
+			header Abc "123"
+			header Bcd "123"
+		}
+	}
+	respond @test 403
+  `, "caddyfile", `{
+	"apps": {
+		"http": {
+			"servers": {
+				"srv0": {
+					"listen": [
+						":80"
+					],
+					"routes": [
+						{
+							"match": [
+								{
+									"not": [
+										{
+											"header": {
+												"Abc": [
+													"123"
+												],
+												"Bcd": [
+													"123"
+												]
+											}
+										}
+									]
+								}
+							],
+							"handle": [
+								{
+									"handler": "static_response",
+									"status_code": 403
+								}
+							]
+						}
+					]
+				}
+			}
+		}
+	}
+}`)
+}
diff --git a/modules/caddyhttp/matchers.go b/modules/caddyhttp/matchers.go
index 95100d58..08607803 100644
--- a/modules/caddyhttp/matchers.go
+++ b/modules/caddyhttp/matchers.go
@@ -592,8 +592,17 @@ func (m *MatchNot) UnmarshalCaddyfile(d *caddyfile.Dispenser) error {
 	for d.Next() {
 		var mp matcherPair
 		matcherMap := make(map[string]RequestMatcher)
-		for d.NextArg() || d.NextBlock(0) {
+
+		// in case there are multiple instances of the same matcher, concatenate
+		// their tokens (we expect that UnmarshalCaddyfile should be able to
+		// handle more than one segment); otherwise, we'd overwrite other
+		// instances of the matcher in this set
+		tokensByMatcherName := make(map[string][]caddyfile.Token)
+		for nesting := d.Nesting(); d.NextArg() || d.NextBlock(nesting); {
 			matcherName := d.Val()
+			tokensByMatcherName[matcherName] = append(tokensByMatcherName[matcherName], d.NextSegment()...)
+		}
+		for matcherName, tokens := range tokensByMatcherName {
 			mod, err := caddy.GetModule("http.matchers." + matcherName)
 			if err != nil {
 				return d.Errf("getting matcher module '%s': %v", matcherName, err)
@@ -602,11 +611,14 @@ func (m *MatchNot) UnmarshalCaddyfile(d *caddyfile.Dispenser) error {
 			if !ok {
 				return d.Errf("matcher module '%s' is not a Caddyfile unmarshaler", matcherName)
 			}
-			err = unm.UnmarshalCaddyfile(d.NewFromNextSegment())
+			err = unm.UnmarshalCaddyfile(caddyfile.NewDispenser(tokens))
 			if err != nil {
 				return err
 			}
-			rm := unm.(RequestMatcher)
+			rm, ok := unm.(RequestMatcher)
+			if !ok {
+				return fmt.Errorf("matcher module '%s' is not a request matcher", matcherName)
+			}
 			matcherMap[matcherName] = rm
 			mp.decoded = append(mp.decoded, rm)
 		}