diff --git a/jsoncpp.spec b/jsoncpp.spec
index 0ed610b..e920dfb 100644
--- a/jsoncpp.spec
+++ b/jsoncpp.spec
@@ -102,6 +102,8 @@ hardlink -cfv %{buildroot}%{_docdir}/%{name}
 
 
 %check
+# Run tests single threaded.
+%global _smp_mflags -j1
 %ctest
 
 
@@ -137,6 +139,7 @@ hardlink -cfv %{buildroot}%{_docdir}/%{name}
 * Sun Sep 27 16:25:23 CEST 2020 Björn Esser <besser82@fedoraproject.org> - 1.9.4-1
 - Update to version 1.9.4 (rhbz#1882874)
 - Package all files generated by doxygen
+- Run tests single threaded
 
 * Wed Jul 29 2020 Björn Esser <besser82@fedoraproject.org> - 1.9.3-3
 - Use new cmake macros