diff --git a/src/main/resources/com/adobe/epubcheck/schema/30/package-30.sch b/src/main/resources/com/adobe/epubcheck/schema/30/package-30.sch
index de969e3fd..07507cea1 100644
--- a/src/main/resources/com/adobe/epubcheck/schema/30/package-30.sch
+++ b/src/main/resources/com/adobe/epubcheck/schema/30/package-30.sch
@@ -274,6 +274,14 @@
+
+
+ The value of the media:duration property must be a valid SMIL3 clock value
+
+
+
diff --git a/src/test/resources/epub3/files/package-document/mediaoverlays-duration-clock-values-error.opf b/src/test/resources/epub3/files/package-document/mediaoverlays-duration-clock-values-error.opf
new file mode 100644
index 000000000..dd59b6885
--- /dev/null
+++ b/src/test/resources/epub3/files/package-document/mediaoverlays-duration-clock-values-error.opf
@@ -0,0 +1,23 @@
+
+
+
+ Title
+ en
+ NOID
+ 2019-01-01T12:00:00Z
+
+ 0:01:30,200
+ 0:9999:12.121
+ 45mon
+
+
+
+
+
+
+
+
+
+
+
\ No newline at end of file
diff --git a/src/test/resources/epub3/mediaoverlays-package-document.feature b/src/test/resources/epub3/mediaoverlays-package-document.feature
index 0910087ed..d71eddcaa 100644
--- a/src/test/resources/epub3/mediaoverlays-package-document.feature
+++ b/src/test/resources/epub3/mediaoverlays-package-document.feature
@@ -59,3 +59,12 @@ Feature: EPUB 3 ▸ Media Overlays ▸ Package Document Checks
Then error RSC-005 is reported
And the message contains "must not be used with the media:playback-active-class property"
And no other errors or warnings are reported
+
+ Scenario: Report 'media:duration' properties with non-clock values
+ When checking file 'mediaoverlays-duration-clock-values-error.opf'
+ Then the following errors are reported
+ | RSC-005 | must be a valid SMIL3 clock value |
+ | RSC-005 | must be a valid SMIL3 clock value |
+ | RSC-005 | must be a valid SMIL3 clock value |
+ And no other errors or warnings are reported
+