diff --git a/libraries/libmp4v2/libmp4v2.SlackBuild b/libraries/libmp4v2/libmp4v2.SlackBuild
index 83ae87475d..fe7d7a6279 100644
--- a/libraries/libmp4v2/libmp4v2.SlackBuild
+++ b/libraries/libmp4v2/libmp4v2.SlackBuild
@@ -38,7 +38,7 @@ cd $(dirname $0) ; CWD=$(pwd)
 
 PRGNAM=libmp4v2
 VERSION=${VERSION:-20191108_9084868}
-BUILD=${BUILD:-1}
+BUILD=${BUILD:-2}
 TAG=${TAG:-_SBo}
 PKGTYPE=${PKGTYPE:-tgz}
 
@@ -91,8 +91,8 @@ find -L . \
  \( -perm 666 -o -perm 664 -o -perm 640 -o -perm 600 -o -perm 444 \
   -o -perm 440 -o -perm 400 \) -exec chmod 644 {} \;
 
-# thanks to Gentoo!
-patch -p1 < $CWD/libmp4v2-2.0.0-unsigned-int-cast.patch
+# Fix gcc 'narrowing errors":
+patch -p1 < "$CWD/libmp4v2_gcc_narrowing.patch" || exit 1
 
 autoreconf -vif
 
diff --git a/libraries/libmp4v2/libmp4v2_gcc_narrowing.patch b/libraries/libmp4v2/libmp4v2_gcc_narrowing.patch
new file mode 100644
index 0000000000..7c3bf692d3
--- /dev/null
+++ b/libraries/libmp4v2/libmp4v2_gcc_narrowing.patch
@@ -0,0 +1,20 @@
+# 
+# libmp4v2_narrowing.patch
+#
+# Reduce LC_NONE by a power of 2 to prevent LongCode promotion to unsigned int
+# causing "narrowing" errors in recent GCC. The value is still sufficiently high
+# as not to clash with any character values.
+#
+
+diff -Nurp libmp4v2-20191108_9084868.orig/libutil/Utility.h libmp4v2-20191108_9084868/libutil/Utility.h
+--- libmp4v2-20191108_9084868.orig/libutil/Utility.h	2019-11-08 02:03:40.000000000 +0000
++++ libmp4v2-20191108_9084868/libutil/Utility.h	2021-08-19 23:40:34.724030480 +0100
+@@ -52,7 +52,7 @@ class MP4V2_EXPORT Utility
+ {
+ protected:
+     enum LongCode {
+-        LC_NONE = 0xf0000000, // safe (cannot conflict with char values)
++        LC_NONE = 0x0f000000, // safe (cannot conflict with char values)
+         LC_DEBUG,
+         LC_VERBOSE,
+         LC_HELP,