diff --git a/src/core/unit-printf.c b/src/core/unit-printf.c
index ffa12d8a92..2daaaf9971 100644
--- a/src/core/unit-printf.c
+++ b/src/core/unit-printf.c
@@ -171,7 +171,7 @@ static int specifier_special_directory(char specifier, const void *data, const v
         return 0;
 }
 
-int unit_name_printf(Unit *u, const char* format, char **ret) {
+int unit_name_printf(const Unit *u, const char* format, char **ret) {
 
         /*
          * This will use the passed string as format string and replace the following specifiers (which should all be
@@ -215,8 +215,7 @@ int unit_name_printf(Unit *u, const char* format, char **ret) {
         return specifier_printf(format, table, u, ret);
 }
 
-int unit_full_printf(Unit *u, const char *format, char **ret) {
-
+int unit_full_printf(const Unit *u, const char *format, char **ret) {
         /* This is similar to unit_name_printf() but also supports unescaping. Also, adds a couple of additional codes
          * (which are likely not suitable for unescaped inclusion in unit names):
          *
diff --git a/src/core/unit-printf.h b/src/core/unit-printf.h
index f3dae159d5..cb75448ae5 100644
--- a/src/core/unit-printf.h
+++ b/src/core/unit-printf.h
@@ -3,5 +3,5 @@
 
 #include "unit.h"
 
-int unit_name_printf(Unit *u, const char* text, char **ret);
-int unit_full_printf(Unit *u, const char *text, char **ret);
+int unit_name_printf(const Unit *u, const char* text, char **ret);
+int unit_full_printf(const Unit *u, const char *text, char **ret);