diff --git a/configure.ac b/configure.ac
index c605c112..6b280a60 100644
--- a/configure.ac
+++ b/configure.ac
@@ -261,6 +261,7 @@ CC_CHECK_FLAGS_APPEND(with_cflags, [CFLAGS], [\
 		       -fdiagnostics-show-option \
 		       -ffunction-sections \
 		       -fno-common \
+		       -funsigned-char \
 		       -fvisibility=hidden \
 		       -W \
 		       -Wall \
diff --git a/meson.build b/meson.build
index 905342c2..9dcaf0ed 100644
--- a/meson.build
+++ b/meson.build
@@ -116,6 +116,7 @@ add_project_arguments(
     '-fdiagnostics-show-option',
     '-ffunction-sections',
     '-fno-common',
+    '-funsigned-char',
     '-Wchar-subscripts',
     '-Wdeclaration-after-statement',
     '-Wendif-labels',