diff --git a/src/USER-MESO/fix_edpd_source.cpp b/src/USER-MESO/fix_edpd_source.cpp
index 56e855ad0c80fa7a0fec7d381976a39d685d85e3..8b03e051814ffe6f636f01d7c8e92f4b83950464 100644
--- a/src/USER-MESO/fix_edpd_source.cpp
+++ b/src/USER-MESO/fix_edpd_source.cpp
@@ -112,7 +112,7 @@ void FixEDPDSource::post_force(int vflag)
         drx = x[i][0] - center[0];
         dry = x[i][1] - center[1];
         drz = x[i][2] - center[2];
-        if(abs(drx) <= 0.5*dLx && abs(dry) <= 0.5*dLy && abs(drz) <= 0.5*dLz)
+        if(fabs(drx) <= 0.5*dLx && fabs(dry) <= 0.5*dLy && fabs(drz) <= 0.5*dLz)
           edpd_flux[i] += value*edpd_cv[i];
       }
     }
diff --git a/src/USER-MESO/fix_tdpd_source.cpp b/src/USER-MESO/fix_tdpd_source.cpp
index 21fecdf49d8c03848cbd45a89e77140c1c843468..64964a4c983ebb5ef8fb5cd27df15079f8860464 100644
--- a/src/USER-MESO/fix_tdpd_source.cpp
+++ b/src/USER-MESO/fix_tdpd_source.cpp
@@ -112,7 +112,7 @@ void FixTDPDSource::post_force(int vflag)
         drx = x[i][0] - center[0];
         dry = x[i][1] - center[1];
         drz = x[i][2] - center[2];
-        if(abs(drx) <= 0.5*dLx && abs(dry) <= 0.5*dLy && abs(drz) <= 0.5*dLz)
+        if(fabs(drx) <= 0.5*dLx && fabs(dry) <= 0.5*dLy && fabs(drz) <= 0.5*dLz)
           cc_flux[i][cc_index-1] += value;
       }
     }