diff --git a/pipi/measure.c b/pipi/measure.c
index c094e64..4ebd35d 100644
--- a/pipi/measure.c
+++ b/pipi/measure.c
@@ -25,6 +25,11 @@
 #include "pipi_internals.h"
 
 double pipi_measure_rmsd(pipi_image_t *i1, pipi_image_t *i2)
+{
+    return sqrt(pipi_measure_msd(i1, i2));
+}
+
+double pipi_measure_msd(pipi_image_t *i1, pipi_image_t *i2)
 {
     pipi_format_t f1, f2;
     double ret = 0.0;
@@ -57,6 +62,6 @@ double pipi_measure_rmsd(pipi_image_t *i1, pipi_image_t *i2)
     i1->last_modified = f1;
     i2->last_modified = f2;
 
-    return sqrt(ret / (w * h));
+    return ret / (w * h);
 }
 
diff --git a/pipi/pipi.h b/pipi/pipi.h
index 6642569..f06e982 100644
--- a/pipi/pipi.h
+++ b/pipi/pipi.h
@@ -59,6 +59,7 @@ extern void pipi_save(pipi_image_t *, const char *);
 
 extern pipi_pixels_t *pipi_getpixels(pipi_image_t *, pipi_format_t);
 
+extern double pipi_measure_msd(pipi_image_t *, pipi_image_t *);
 extern double pipi_measure_rmsd(pipi_image_t *, pipi_image_t *);
 
 extern pipi_image_t *pipi_resize(pipi_image_t *, int, int);