diff --git a/.travis.yml b/.travis.yml
index 6b732fb6c9..f32778b3a2 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -104,6 +104,16 @@ script:
   - opt_enable EEPROM_SETTINGS EEPROM_CHITCHAT
   - build_marlin
   #
+  # Test DUAL_X_CARRIAGE
+  #
+  - restore_configs
+  - opt_set MOTHERBOARD BOARD_RAMPS_14_EEB
+  - opt_set EXTRUDERS 2
+  - opt_set TEMP_SENSOR_1 1
+  - opt_enable USE_XMAX_PLUG
+  - opt_enable_adv DUAL_X_CARRIAGE
+  - build_marlin
+  #
   ### LCDS ###
   #
   #
diff --git a/Marlin/Marlin.h b/Marlin/Marlin.h
index 04064701e9..d5bd54f077 100644
--- a/Marlin/Marlin.h
+++ b/Marlin/Marlin.h
@@ -129,6 +129,10 @@ void idle(
 
 void manage_inactivity(bool ignore_stepper_queue = false);
 
+#if ENABLED(DUAL_X_CARRIAGE)
+  extern bool extruder_duplication_enabled;
+#endif
+
 #if ENABLED(DUAL_X_CARRIAGE) && HAS_X_ENABLE && HAS_X2_ENABLE
   #define  enable_x() do { X_ENABLE_WRITE( X_ENABLE_ON); X2_ENABLE_WRITE( X_ENABLE_ON); } while (0)
   #define disable_x() do { X_ENABLE_WRITE(!X_ENABLE_ON); X2_ENABLE_WRITE(!X_ENABLE_ON); axis_known_position[X_AXIS] = false; } while (0)
diff --git a/Marlin/SanityCheck.h b/Marlin/SanityCheck.h
index c45c716141..c499c2c967 100644
--- a/Marlin/SanityCheck.h
+++ b/Marlin/SanityCheck.h
@@ -398,14 +398,18 @@
  * Dual X Carriage requirements
  */
 #if ENABLED(DUAL_X_CARRIAGE)
-  #if EXTRUDERS == 1 || ENABLED(COREXY) \
-      || !HAS_X2_ENABLE || !HAS_X2_STEP || !HAS_X2_DIR \
-      || !defined(X2_HOME_POS) || !defined(X2_MIN_POS) || !defined(X2_MAX_POS) \
-      || !HAS_X_MAX
-    #error "Missing or invalid definitions for DUAL_X_CARRIAGE mode."
-  #endif
-  #if X_HOME_DIR != -1 || X2_HOME_DIR != 1
-    #error "Please use canonical x-carriage assignment."
+  #if EXTRUDERS == 1
+    #error "DUAL_X_CARRIAGE requires 2 (or more) extruders."
+  #elif ENABLED(COREXY) || ENABLED(COREXZ)
+    #error "DUAL_X_CARRIAGE cannot be used with COREXY or COREXZ."
+  #elif !HAS_X2_ENABLE || !HAS_X2_STEP || !HAS_X2_DIR
+    #error "DUAL_X_CARRIAGE requires X2 stepper pins to be defined."
+  #elif !HAS_X_MAX
+    #error "DUAL_X_CARRIAGE requires USE_XMAX_PLUG and an X Max Endstop."
+  #elif !defined(X2_HOME_POS) || !defined(X2_MIN_POS) || !defined(X2_MAX_POS)
+    #error "DUAL_X_CARRIAGE requires X2_HOME_POS, X2_MIN_POS, and X2_MAX_POS."
+  #elif X_HOME_DIR != -1 || X2_HOME_DIR != 1
+    #error "DUAL_X_CARRIAGE requires X_HOME_DIR -1 and X2_HOME_DIR 1."
   #endif
 #endif // DUAL_X_CARRIAGE
 
diff --git a/Marlin/planner.h b/Marlin/planner.h
index e1dc8941af..bd178d2577 100644
--- a/Marlin/planner.h
+++ b/Marlin/planner.h
@@ -165,10 +165,6 @@ class Planner {
       static long axis_segment_time[2][3] = { {MAX_FREQ_TIME + 1, 0, 0}, {MAX_FREQ_TIME + 1, 0, 0} };
     #endif
 
-    #if ENABLED(DUAL_X_CARRIAGE)
-      extern bool extruder_duplication_enabled;
-    #endif
-
   public:
 
     Planner();
diff --git a/Marlin/stepper_indirection.h b/Marlin/stepper_indirection.h
index 0a534efdd7..c013d268e3 100644
--- a/Marlin/stepper_indirection.h
+++ b/Marlin/stepper_indirection.h
@@ -193,7 +193,6 @@
     #define NORM_E_DIR() _NORM_E_DIR()
     #define REV_E_DIR() _REV_E_DIR()
   #else
-    extern bool extruder_duplication_enabled;
     #define E_STEP_WRITE(v) {if(extruder_duplication_enabled){E0_STEP_WRITE(v);E1_STEP_WRITE(v);}else _E_STEP_WRITE(v);}
     #define NORM_E_DIR() {if(extruder_duplication_enabled){E0_DIR_WRITE(!INVERT_E0_DIR);E1_DIR_WRITE(!INVERT_E1_DIR);}else _NORM_E_DIR();}
     #define REV_E_DIR() {if(extruder_duplication_enabled){E0_DIR_WRITE(INVERT_E0_DIR);E1_DIR_WRITE(INVERT_E1_DIR);}else _REV_E_DIR();}