diff --git a/owlps-positioning/src/multilaterationalgorithm.cc b/owlps-positioning/src/multilaterationalgorithm.cc
index 4ef19ce..edc03da 100644
--- a/owlps-positioning/src/multilaterationalgorithm.cc
+++ b/owlps-positioning/src/multilaterationalgorithm.cc
@@ -43,7 +43,7 @@ make_constant_term(const Measurement &measurement)
     ap->get_trx_power() +
     ap->get_antenna_gain() +
     20 * log10(
-      300000000.0 /
+      static_cast<double>(PosUtil::LIGHT_SPEED) /
       ap->get_frequency() /
       (4 * M_PI)
     ) +
diff --git a/owlps-positioning/src/posutil.hh b/owlps-positioning/src/posutil.hh
index 16f46ab..aa66643 100644
--- a/owlps-positioning/src/posutil.hh
+++ b/owlps-positioning/src/posutil.hh
@@ -5,6 +5,9 @@
 class PosUtil
 {
 public:
+  /// The speed of light, in m/s
+  static const unsigned long LIGHT_SPEED = 299792458 ;
+
   /** @name Wi-Fi */
   //@{
   /// Converts a Wi-Fi channel to the corresponding frequency in Hz
diff --git a/owlps-positioning/tests/interlinknetworks_test.hh b/owlps-positioning/tests/interlinknetworks_test.hh
index 7b95d20..beda92f 100644
--- a/owlps-positioning/tests/interlinknetworks_test.hh
+++ b/owlps-positioning/tests/interlinknetworks_test.hh
@@ -24,11 +24,11 @@ public:
     Measurement measurement(&ap, ss_list) ;
 
     /* ** How to check ref_distance in Scilab? **
-     * C = 5 + 20 + 20 * log10(300000000 / 2412000000 / (4 * PI)) + 3
+     * C = 5 + 20 + 20 * log10(299792458 / 2412000000 / (4 * PI)) + 3
      * L = -42
      * ref_distance = 10^((C-L)/35)
      */
-    float ref_distance = 7.1547 ;
+    float ref_distance = 7.1519 ;
 
     float computed_distance = algo->estimate_distance(measurement) ;
     TS_ASSERT_DELTA(computed_distance, ref_distance, 0.0001) ;