diff --git a/src/ppp.c b/src/ppp.c
index 385dc9990..c85773881 100644
--- a/src/ppp.c
+++ b/src/ppp.c
@@ -958,6 +958,7 @@ static int ppp_res(int post, const obsd_t *obs, int n, const double *rs,
     for (i=0;i<n&&i<MAXOBS;i++) {
         sat=obs[i].sat;
 
+        /* line-of-sight vector from receiver to satellite */
         if ((r=geodist(rs+i*6,rr,e))<=0.0||
             satazel(pos,e,azel+i*2)<opt->elmin) {
             exc[i]=1;
@@ -1030,7 +1031,7 @@ static int ppp_res(int post, const obsd_t *obs, int n, const double *rs,
             if (opt->ionoopt==IONOOPT_EST) {
                 if (rtk->x[II(sat,opt)]==0.0) continue;
                 /* The vertical iono delay is estimated, but the residual is
-                 * in the direction of the slant, so apply the slat factor
+                 * in the direction of the slant, so apply the slant factor
                  * mapping function. */
                 if (H) H[II(sat,opt)+nx*nv]=C*ionmapf(pos,azel+i*2);
             }
@@ -1051,23 +1052,24 @@ static int ppp_res(int post, const obsd_t *obs, int n, const double *rs,
 
             /* variance */
             var[nv]=varerr(sat,sys,azel[1+i*2],
-                    rtk->ssat[sat-1].snr_rover[frq],
-                    j,opt,obs+i);
+                           rtk->ssat[sat-1].snr_rover[frq],
+                           j,opt,obs+i);
             var[nv] +=vart+SQR(C)*vari+var_rs[i];
             if (sys==SYS_GLO&&code==1) var[nv]+=VAR_GLO_IFB;
 
-            trace(3,"%s sat=%2d %s%d res=%9.4f sig=%9.4f el=%4.1f\n",str,sat,
-                  code?"P":"L",frq+1,res,sqrt(var[nv]),azel[1+i*2]*R2D);
+            trace(3,"%s post=%2d sat=%2d %s%d res=%9.4f sig=%9.4f el=%4.1f\n",
+                  str,post,sat,code?"P":"L",frq+1,res,sqrt(var[nv]),azel[1+i*2]*R2D);
 
             /* reject satellite by pre-fit residuals */
-            if (!post&&opt->maxinno[code]>0.0&&fabs(res)>opt->maxinno[code]) {
+            double maxinno = (post==-1?1000:1)*opt->maxinno[code];
+            if (post<=0&&opt->maxinno[code]>0.0&&fabs(res)>maxinno) {
                 trace(2,"outlier (%d) rejected %s sat=%2d %s%d res=%9.4f el=%4.1f\n",
                       post,str,sat,code?"P":"L",frq+1,res,azel[1+i*2]*R2D);
                 exc[i]=1; rtk->ssat[sat-1].rejc[frq]++;
                 continue;
             }
             /* record large post-fit residuals */
-            if (post&&fabs(res)>sqrt(var[nv])*THRES_REJECT) {
+            if (post>0&&fabs(res)>sqrt(var[nv])*THRES_REJECT) {
                 obsi[ne]=i; frqi[ne]=j; ve[ne]=res; ne++;
             }
             if (code==0) rtk->ssat[sat-1].vsat[frq]=1;
@@ -1075,7 +1077,7 @@ static int ppp_res(int post, const obsd_t *obs, int n, const double *rs,
         }
     }
     /* reject satellite with large and max post-fit residual */
-    if (post&&ne>0) {
+    if (post>0&&ne>0) {
         vmax=ve[0]; maxobs=obsi[0]; maxfrq=frqi[0]; rej=0;
         for (j=1;j<ne;j++) {
             if (fabs(vmax)>=fabs(ve[j])) continue;
@@ -1083,7 +1085,7 @@ static int ppp_res(int post, const obsd_t *obs, int n, const double *rs,
         }
         sat=obs[maxobs].sat;
         trace(2,"outlier (%d) rejected %s sat=%2d %s%d res=%9.4f el=%4.1f\n",
-            post,str,sat,maxfrq%2?"P":"L",maxfrq/2+1,vmax,azel[1+maxobs*2]*R2D);
+              post,str,sat,maxfrq%2?"P":"L",maxfrq/2+1,vmax,azel[1+maxobs*2]*R2D);
         exc[maxobs]=1; rtk->ssat[sat-1].rejc[maxfrq%2]++; stat=0;
         ve[rej]=0;
     }
@@ -1091,7 +1093,7 @@ static int ppp_res(int post, const obsd_t *obs, int n, const double *rs,
         for (j=0;j<nv;j++) for (i=0;i<nv;i++) R[i+j*nv]=0.0;
         for (i=0;i<nv;i++) R[i+i*nv]=var[i];
     }
-    return post?stat:nv;
+    return post>0?stat:nv;
 }
 /* number of estimated states ------------------------------------------------*/
 extern int pppnx(const prcopt_t *opt)
@@ -1225,8 +1227,11 @@ extern void pppos(rtk_t *rtk, const obsd_t *obs, int n, const nav_t *nav)
         matcpy(xp,rtk->x,rtk->nx,1);
         matcpy(Pp,rtk->P,rtk->nx,rtk->nx);
 
-        /* prefit residuals */
-        if (!(nv=ppp_res(0,obs,n,rs,dts,var,svh,dr,exc,nav,xp,rtk,v,H,R,azel))) {
+        /* prefit residuals
+         * NOTE: use different limit for pre-fit residuals in first iteration
+         *       by using argument post = -1
+         */
+        if (!(nv=ppp_res(i==0?-1:0,obs,n,rs,dts,var,svh,dr,exc,nav,xp,rtk,v,H,R,azel))) {
             trace(2,"%s ppp (%d) no valid obs data\n",str,i+1);
             break;
         }