diff --git a/CMakeLists.txt b/CMakeLists.txt
index 5f50f77..000817d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -23,6 +23,7 @@ set(SOURCES
   # ctype
   src/ctype/charprops.c
   src/ctype/classes.c
+  src/ctype/convert.c
   # string
   src/string/memarray.c
   src/string/core.c
diff --git a/include/ft/all-tests.h b/include/ft/all-tests.h
index 7fef70f..5540ad3 100644
--- a/include/ft/all-tests.h
+++ b/include/ft/all-tests.h
@@ -10,6 +10,8 @@
 /* ctype */
 extern ft_test ft_ctype_macros;
 extern ft_test ft_ctype_functions;
+extern ft_test ft_ctype_convert_macros;
+extern ft_test ft_ctype_convert_functions;
 
 /* string */
 extern ft_test ft_string_memset;
diff --git a/src/ctype/classes.c b/src/ctype/classes.c
index 7ee4176..0cb8c0d 100644
--- a/src/ctype/classes.c
+++ b/src/ctype/classes.c
@@ -23,7 +23,7 @@ static void _ctype_macros(ft_test *t)
 }
 
 ft_test ft_ctype_macros = {
-    .name = "Macro versions of functions",
+    .name = "Macro-based classification",
     .function = _ctype_macros,
 };
 
@@ -61,6 +61,6 @@ static void _ctype_functions(ft_test *t)
 }
 
 ft_test ft_ctype_functions = {
-    .name = "Pure functions",
+    .name = "Function-based classification",
     .function = _ctype_functions,
 };
diff --git a/src/ctype/convert.c b/src/ctype/convert.c
new file mode 100644
index 0000000..c612ae0
--- /dev/null
+++ b/src/ctype/convert.c
@@ -0,0 +1,38 @@
+#include <ft/test.h>
+#include <ft/all-tests.h>
+#include <ctype.h>
+
+static void _ctype_convert_macros(ft_test *t)
+{
+	for(int c = 0; c < 128; c++) {
+		int cl = (isupper(c) ? c - 'A' + 'a' : c);
+		int cu = (islower(c) ? c - 'a' + 'A' : c);
+
+		ft_assert(t, tolower(c) == cl);
+		ft_assert(t, toupper(c) == cu);
+	}
+}
+
+ft_test ft_ctype_convert_macros = {
+	.name = "Macro-based conversion",
+	.function = _ctype_convert_macros,
+};
+
+#undef tolower
+#undef toupper
+
+static void _ctype_convert_functions(ft_test *t)
+{
+	for(int c = 0; c < 128; c++) {
+		int cl = (isupper(c) ? c - 'A' + 'a' : c);
+		int cu = (islower(c) ? c - 'a' + 'A' : c);
+
+		ft_assert(t, tolower(c) == cl);
+		ft_assert(t, toupper(c) == cu);
+	}
+}
+
+ft_test ft_ctype_convert_functions = {
+	.name = "Function-based conversion",
+	.function = _ctype_convert_functions,
+};
diff --git a/src/main.c b/src/main.c
index ccd63fb..ff2cc5b 100644
--- a/src/main.c
+++ b/src/main.c
@@ -16,6 +16,8 @@ ft_list headers_libc[] = {
     { "<ctype.h>", (ft_test*[]){
         &ft_ctype_macros,
         &ft_ctype_functions,
+        &ft_ctype_convert_macros,
+        &ft_ctype_convert_functions,
         NULL,
     }},
     { "<locale.h>", NULL },