diff --git a/common/expression.cpp b/common/expression.cpp
index 1671d04b..821cb7f5 100644
--- a/common/expression.cpp
+++ b/common/expression.cpp
@@ -38,7 +38,7 @@ Expression::Expression(double initial) : value(initial)
         default_functions->insert("log", [](double a) { return log(a); });
         default_functions->insert("log10", [](double a) { return log(a); });
         default_functions->insert("trunc", [](double a) { return trunc(a); });
-        default_functions->insert("abs", [](double a) { return abs(a); });
+        default_functions->insert("abs", [](double a) { return fabs(a); });
 
         default_functions->insert("floor", [](double a) { return floor(a); });
         default_functions->insert("ceil", [](double a) { return ceil(a); });