diff --git a/src/compiler/glsl/glcpp/meson.build b/src/compiler/glsl/glcpp/meson.build
index bc4eda26a76..bc892604ff0 100644
--- a/src/compiler/glsl/glcpp/meson.build
+++ b/src/compiler/glsl/glcpp/meson.build
@@ -85,6 +85,13 @@ if with_any_opengl and with_tests and host_machine.system() != 'windows'
     modes += ['valgrind']
   endif
 
+  # For some unfathomable reason, three out of these four tests often time out
+  # when running within CI. On the assumption that there is some
+  # parallelisation badness happening rather than the non-UNIX tests entering
+  # infinite loops, try just marking them as serial-only.
+  #
+  # This should have a negligible impact on runtime since they are quick to
+  # execute.
   foreach m : modes
     test(
       'glcpp test (@0@)'.format(m),
@@ -96,6 +103,7 @@ if with_any_opengl and with_tests and host_machine.system() != 'windows'
       ],
       suite : ['compiler', 'glcpp'],
       timeout: 60,
+      is_parallel: false,
     )
   endforeach
 endif