diff --git a/lib/rtl/rtl_source_c.cc b/lib/rtl/rtl_source_c.cc
index 93328b8..97252a7 100644
--- a/lib/rtl/rtl_source_c.cc
+++ b/lib/rtl/rtl_source_c.cc
@@ -661,7 +661,7 @@ double rtl_source_c::set_if_gain(double gain, size_t chan)
           sum += gains[ j + 1 ];
       }
 
-      double err = abs(gain - sum);
+      double err = std::abs(gain - sum);
       if (err < error) {
         error = err;
         gains[ i + 1 ] = g;
diff --git a/lib/rtl_tcp/rtl_tcp_source_c.cc b/lib/rtl_tcp/rtl_tcp_source_c.cc
index a365688..1b2c533 100644
--- a/lib/rtl_tcp/rtl_tcp_source_c.cc
+++ b/lib/rtl_tcp/rtl_tcp_source_c.cc
@@ -432,7 +432,7 @@ double rtl_tcp_source_c::set_if_gain(double gain, size_t chan)
           sum += gains[ j + 1 ];
       }
 
-      double err = abs(gain - sum);
+      double err = std::abs(gain - sum);
       if (err < error) {
         error = err;
         gains[ i + 1 ] = g;