diff --git a/src/main/java/com/adobe/epubcheck/xml/handlers/DeclarationHandler.java b/src/main/java/com/adobe/epubcheck/xml/handlers/DeclarationHandler.java
index aab950a46..732cca9c0 100644
--- a/src/main/java/com/adobe/epubcheck/xml/handlers/DeclarationHandler.java
+++ b/src/main/java/com/adobe/epubcheck/xml/handlers/DeclarationHandler.java
@@ -134,6 +134,10 @@ else if (publicId != null || systemId != null)
isAllowed = "-//W3C//DTD MathML 3.0//EN".equals(publicId)
&& "http://www.w3.org/Math/DTD/mathml3/mathml3.dtd".equals(systemId);
break;
+ case "application/x-dtbncx+xml":
+ isAllowed = "-//NISO//DTD ncx 2005-1//EN".equals(publicId)
+ && "http://www.daisy.org/z3986/2005/ncx-2005-1.dtd".equals(systemId);
+ break;
default:
isAllowed = false;
}
diff --git a/src/test/resources/epub3/B-external-identifiers/external-identifiers.feature b/src/test/resources/epub3/B-external-identifiers/external-identifiers.feature
index 59fbf7ae4..55dc4fa27 100644
--- a/src/test/resources/epub3/B-external-identifiers/external-identifiers.feature
+++ b/src/test/resources/epub3/B-external-identifiers/external-identifiers.feature
@@ -10,7 +10,7 @@
Given EPUB test files located at '/epub3/B-external-identifiers/files/'
And EPUBCheck with default settings
-
+ @spec @xref:app-identifiers-allowed
Scenario: Verify DOCTYPE declarations with allowed external identifiers
When checking EPUB 'xml-external-identifier-allowed-valid'
Then no errors or warnings are reported
diff --git a/src/test/resources/epub3/B-external-identifiers/files/xml-external-identifier-allowed-valid/EPUB/nav.ncx b/src/test/resources/epub3/B-external-identifiers/files/xml-external-identifier-allowed-valid/EPUB/nav.ncx
new file mode 100644
index 000000000..ea192b3ba
--- /dev/null
+++ b/src/test/resources/epub3/B-external-identifiers/files/xml-external-identifier-allowed-valid/EPUB/nav.ncx
@@ -0,0 +1,24 @@
+
+
+
+
+
+
+
+
+
+
+ NCX
+
+
+
+
+ Chapter 1
+
+
+
+
+
\ No newline at end of file
diff --git a/src/test/resources/epub3/B-external-identifiers/files/xml-external-identifier-allowed-valid/EPUB/package.opf b/src/test/resources/epub3/B-external-identifiers/files/xml-external-identifier-allowed-valid/EPUB/package.opf
index f89109202..a71e6bc10 100644
--- a/src/test/resources/epub3/B-external-identifiers/files/xml-external-identifier-allowed-valid/EPUB/package.opf
+++ b/src/test/resources/epub3/B-external-identifiers/files/xml-external-identifier-allowed-valid/EPUB/package.opf
@@ -13,8 +13,9 @@