diff --git a/src/COLLOID/pair_colloid.cpp b/src/COLLOID/pair_colloid.cpp
index e9e4bfdd2d..6d83e3bd07 100644
--- a/src/COLLOID/pair_colloid.cpp
+++ b/src/COLLOID/pair_colloid.cpp
@@ -148,6 +148,7 @@ void PairColloid::compute(int eflag, int vflag)
 	  evdwl = 2.0/9.0*fR * 
 	    (1.0-(K[1]*(K[1]*(K[1]/3.0+3.0*K[2])+4.2*K[4])+K[2]*K[4]) *
 	     sigma6[itype][jtype]/K[6]) - offset[itype][jtype];
+	if (rsq <= K[1]) error->one("Overlapping small/large in pair colloid");
 	break;
 
       case LARGE_LARGE:
@@ -185,6 +186,7 @@ void PairColloid::compute(int eflag, int vflag)
 	if (eflag)
 	  evdwl += a12[itype][jtype]/6.0 * 
 	    (2.0*K[0]*(K[7]+K[8])-log(K[8]/K[7])) - offset[itype][jtype];
+	if (r <= K[1]) error->one("Overlapping large/large in pair colloid");
 	break;
       }