diff --git a/firmware/controllers/core/interpolation.cpp b/firmware/controllers/core/interpolation.cpp
index 210d6b1a95..e0d17bb94c 100644
--- a/firmware/controllers/core/interpolation.cpp
+++ b/firmware/controllers/core/interpolation.cpp
@@ -2,6 +2,9 @@
  * @file    interpolation.cpp
  * @brief	Linear interpolation algorithms
  *
+ * See test_interpolation_3d.cpp
+ *
+ *
  * @date Oct 17, 2013
  * @author Andrey Belomutskiy, (c) 2012-2018
  * @author Dmitry Sidin, (c) 2015
diff --git a/unit_tests/test_basic_math/test_interpolation_3d.cpp b/unit_tests/test_basic_math/test_interpolation_3d.cpp
index 588210f66d..8ccc929a6e 100644
--- a/unit_tests/test_basic_math/test_interpolation_3d.cpp
+++ b/unit_tests/test_basic_math/test_interpolation_3d.cpp
@@ -1,12 +1,10 @@
 /*
+ * @file    test_interpolation_3d.cpp
+ *
  *  Created on: Oct 17, 2013
  * @author Andrey Belomutskiy, (c) 2012-2018
  */
 
-/**
- * @file    test_interpolation_3d.c
- */
-
 #include "test_interpolation_3d.h"
 #include <stdlib.h>
 
@@ -61,6 +59,13 @@ static void newTestToComfirmInterpolation() {
 	assertEqualsM("middle @ 2.3  ",35.15, getValue(/*rpm*/250, 2.3));
 
 	assertEqualsM("middle cell    ", 54.25, getValue(/*rpm*/250, 2.5));
+
+	// issue #604: interpolation outside of the table
+	assertEqualsM("800 @ 2.1  ",200, getValue(/*rpm*/800, 2.1));
+	assertEqualsM("800 @ 2.3  ",200, getValue(/*rpm*/800, 2.3));
+	assertEqualsM("800 @ 3.3  ",500, getValue(/*rpm*/800, 3.3));
+
+
 }
 
 void testInterpolate3d(void) {