diff --git a/packages/math.mo b/packages/math.mo
index 856473ec..791af076 100644
--- a/packages/math.mo
+++ b/packages/math.mo
@@ -1,5 +1,11 @@
 package math
 
+function fabs
+    input Real x;
+    output Real y;
+    external "C" y = fabs(x);
+  end fabs;
+
 function random
     input Real x;
     output Real y;
diff --git a/src/mmoc/tests/system/gt_data/packages/math.mo b/src/mmoc/tests/system/gt_data/packages/math.mo
index 856473ec..791af076 100644
--- a/src/mmoc/tests/system/gt_data/packages/math.mo
+++ b/src/mmoc/tests/system/gt_data/packages/math.mo
@@ -1,5 +1,11 @@
 package math
 
+function fabs
+    input Real x;
+    output Real y;
+    external "C" y = fabs(x);
+  end fabs;
+
 function random
     input Real x;
     output Real y;
diff --git a/src/mmoc/tests/system/gt_data/packages/pkg_math.c b/src/mmoc/tests/system/gt_data/packages/pkg_math.c
index a104eb2b..6bc08126 100644
--- a/src/mmoc/tests/system/gt_data/packages/pkg_math.c
+++ b/src/mmoc/tests/system/gt_data/packages/pkg_math.c
@@ -1,6 +1,6 @@
 #include <math.h>
 #include <stdlib.h>
-#include "./system/test_data/packages/pkg_math.h"
+#include "/home/joaquin/work/qss-solver/packages/pkg_math.h"
 #include <mmo_math.h>
 double __math__exponential(double x)
 {
@@ -10,6 +10,14 @@ y = mmo_exponential(x);
 return y;
 }
 
+double __math__fabs(double x)
+{
+double y;
+
+y = fabs(x);
+return y;
+}
+
 double __math__getRandomMarkedValue(double x)
 {
 double y;
diff --git a/src/mmoc/tests/system/gt_data/packages/pkg_math.h b/src/mmoc/tests/system/gt_data/packages/pkg_math.h
index ed138110..9e78ce95 100644
--- a/src/mmoc/tests/system/gt_data/packages/pkg_math.h
+++ b/src/mmoc/tests/system/gt_data/packages/pkg_math.h
@@ -3,6 +3,9 @@
 double __math__exponential(double x);
 
 
+double __math__fabs(double x);
+
+
 double __math__getRandomMarkedValue(double x);
 
 
diff --git a/src/mmoc/tests/system/gt_data/packages/pkg_math.moo b/src/mmoc/tests/system/gt_data/packages/pkg_math.moo
index de029c3b..7e61ac17 100644
--- a/src/mmoc/tests/system/gt_data/packages/pkg_math.moo
+++ b/src/mmoc/tests/system/gt_data/packages/pkg_math.moo
@@ -14,6 +14,17 @@ ENDLIBRARIES
 ENDDEFINITION
 DEFINITION
 FUNCTION
+fabs
+ENDFUNCTION
+INCLUDEDIRECTORY
+/home/joaquin/work/qss-solver/src/usr/include
+ENDINCLUDEDIRECTORY
+LIBRARYDIRECTORY
+/home/joaquin/work/qss-solver/lib
+ENDLIBRARYDIRECTORY
+ENDDEFINITION
+DEFINITION
+FUNCTION
 getRandomMarkedValue
 ENDFUNCTION
 INCLUDEDIRECTORY