diff --git a/Marlin/endstops.cpp b/Marlin/endstops.cpp
index c6c94b87c..53e8b209e 100644
--- a/Marlin/endstops.cpp
+++ b/Marlin/endstops.cpp
@@ -222,7 +222,7 @@ void Endstops::M119() {
 #if ENABLED(Z_DUAL_ENDSTOPS)
 
   // Pass the result of the endstop test
-  void Endstops::test_dual_z_endstops(EndstopEnum es1, EndstopEnum es2) {
+  void Endstops::test_dual_z_endstops(const EndstopEnum es1, const EndstopEnum es2) {
     byte z_test = TEST_ENDSTOP(es1) | (TEST_ENDSTOP(es2) << 1); // bit 0 for Z, bit 1 for Z2
     if (z_test && stepper.current_block->steps[Z_AXIS] > 0) {
       SBI(endstop_hit_bits, Z_MIN);
diff --git a/Marlin/endstops.h b/Marlin/endstops.h
index 22c2468b8..4f2ce9e5d 100644
--- a/Marlin/endstops.h
+++ b/Marlin/endstops.h
@@ -86,7 +86,7 @@ class Endstops {
   private:
 
     #if ENABLED(Z_DUAL_ENDSTOPS)
-      static void test_dual_z_endstops(EndstopEnum es1, EndstopEnum es2);
+      static void test_dual_z_endstops(const EndstopEnum es1, const EndstopEnum es2);
     #endif
 };