diff --git a/valgrind-3.17.0-clone-parent-res.patch b/valgrind-3.17.0-clone-parent-res.patch
new file mode 100644
index 0000000..8d03cea
--- /dev/null
+++ b/valgrind-3.17.0-clone-parent-res.patch
@@ -0,0 +1,21 @@
+commit e08a82991a9b9dc87c13f2b89273f25f97d14baf
+Author: Tom Hughes <tom@compton.nu>
+Date:   Tue Apr 6 22:44:36 2021 +0100
+
+    Only process clone results in the parent thread
+    
+    Fixes BZ#423963
+
+diff --git a/coregrind/m_syswrap/syswrap-linux.c b/coregrind/m_syswrap/syswrap-linux.c
+index 5ae4e6613..c59d8ee26 100644
+--- a/coregrind/m_syswrap/syswrap-linux.c
++++ b/coregrind/m_syswrap/syswrap-linux.c
+@@ -940,7 +940,7 @@ PRE(sys_clone)
+          ("Valgrind does not support general clone().");
+    }
+ 
+-   if (SUCCESS) {
++   if (SUCCESS && RES != 0) {
+       if (ARG_FLAGS & (VKI_CLONE_PARENT_SETTID | VKI_CLONE_PIDFD))
+          POST_MEM_WRITE(ARG3, sizeof(Int));
+       if (ARG_FLAGS & (VKI_CLONE_CHILD_SETTID | VKI_CLONE_CHILD_CLEARTID))
diff --git a/valgrind.spec b/valgrind.spec
index a351b65..57ebbb4 100644
--- a/valgrind.spec
+++ b/valgrind.spec
@@ -113,6 +113,9 @@ Patch8: valgrind-3.17.0-s390_insn_as_string.patch
 # KDE#435908 Don't look for separate debuginfo if image already has .debug_info
 Patch9: valgrind-3.17.0-debuginfod.patch
 
+# KDE#423963 Only process clone results in the parent thread
+Patch10: valgrind-3.17.0-clone-parent-res.patch
+
 BuildRequires: make
 BuildRequires: glibc-devel
 
@@ -259,6 +262,7 @@ Valgrind User Manual for details.
 
 %patch8 -p1
 %patch9 -p1
+%patch10 -p1
 
 %build
 # LTO triggers undefined symbols in valgrind.  Valgrind has a --enable-lto
@@ -487,6 +491,7 @@ fi
 * Thu Jun  3 2021 Mark Wielaard <mjw@fedoraproject.org>
 - Add valgrind-3.17.0-s390_insn_as_string.patch
 - Add valgrind-3.17.0-debuginfod.patch
+- Add valgrind-3.17.0-clone-parent-res.patch
 
 * Tue May  4 2021 Mark Wielaard <mjw@fedoraproject.org> - 3.17.0-3
 - Add valgrind-3.17.0-ppc64-isa-3.1{,tests}.patch