diff --git a/Makefile.am b/Makefile.am
index aca863a..bccf5dd 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -2,6 +2,9 @@
 
 # Ignore system headers
 CODE_COVERAGE_IGNORE_PATTERN = '/include/*' '/usr/include/*' '$(includedir)/*'
+# Ignore the real implementation sources for sys
+CODE_COVERAGE_IGNORE_PATTERN += \
+    '$(abs_builddir)/src/gpioplus/internal/sys.*'
 export CODE_COVERAGE_IGNORE_PATTERN
 
 CODE_COVERAGE_LCOV_SHOPTS = $(CODE_COVERAGE_LCOV_SHOPTS_DEFAULT)