diff --git a/ext/rtree/geopoly.c b/ext/rtree/geopoly.c
index 3adbca7c24..d93eca2309 100644
--- a/ext/rtree/geopoly.c
+++ b/ext/rtree/geopoly.c
@@ -124,6 +124,14 @@ struct GeoPoly {
 */
 #define GEOPOLY_SZ(N)  (sizeof(GeoPoly) + sizeof(GeoCoord)*2*((N)-4))
 
+/* Macros to access coordinates of a GeoPoly.
+** We have to use these macros, rather than just say p->a[i] in order
+** to silence (incorrect) UBSAN warnings if the array index is too large.
+*/
+#define GeoX(P,I)  (((GeoCoord*)(P)->a)[(I)*2])
+#define GeoY(P,I)  (((GeoCoord*)(P)->a)[(I)*2+1])
+
+
 /*
 ** State of a parse of a GeoJSON input.
 */
@@ -316,8 +324,9 @@ static GeoPoly *geopolyFuncParam(
         memcpy(p->hdr, a, nByte);
         if( a[0] != *(unsigned char*)&x ){
           int ii;
-          for(ii=0; ii<nVertex*2; ii++){
-            geopolySwab32((unsigned char*)&p->a[ii]);
+          for(ii=0; ii<nVertex; ii++){
+            geopolySwab32((unsigned char*)&GeoX(p,ii));
+            geopolySwab32((unsigned char*)&GeoY(p,ii));
           }
           p->hdr[0] ^= 1;
         }
@@ -376,9 +385,9 @@ static void geopolyJsonFunc(
     int i;
     sqlite3_str_append(x, "[", 1);
     for(i=0; i<p->nVertex; i++){
-      sqlite3_str_appendf(x, "[%!g,%!g],", p->a[i*2], p->a[i*2+1]);
+      sqlite3_str_appendf(x, "[%!g,%!g],", GeoX(p,i), GeoY(p,i));
     }
-    sqlite3_str_appendf(x, "[%!g,%!g]]", p->a[0], p->a[1]);
+    sqlite3_str_appendf(x, "[%!g,%!g]]", GeoX(p,0), GeoY(p,0));
     sqlite3_result_text(context, sqlite3_str_finish(x), -1, sqlite3_free);
     sqlite3_free(p);
   }
@@ -405,10 +414,10 @@ static void geopolySvgFunc(
     char cSep = '\'';
     sqlite3_str_appendf(x, "<polyline points=");
     for(i=0; i<p->nVertex; i++){
-      sqlite3_str_appendf(x, "%c%g,%g", cSep, p->a[i*2], p->a[i*2+1]);
+      sqlite3_str_appendf(x, "%c%g,%g", cSep, GeoX(p,i), GeoY(p,i));
       cSep = ' ';
     }
-    sqlite3_str_appendf(x, " %g,%g'", p->a[0], p->a[1]);
+    sqlite3_str_appendf(x, " %g,%g'", GeoX(p,0), GeoY(p,0));
     for(i=1; i<argc; i++){
       const char *z = (const char*)sqlite3_value_text(argv[i]);
       if( z && z[0] ){
@@ -453,12 +462,12 @@ static void geopolyXformFunc(
   int ii;
   if( p ){
     for(ii=0; ii<p->nVertex; ii++){
-      x0 = p->a[ii*2];
-      y0 = p->a[ii*2+1];
+      x0 = GeoX(p,ii);
+      y0 = GeoY(p,ii);
       x1 = (GeoCoord)(A*x0 + B*y0 + E);
       y1 = (GeoCoord)(C*x0 + D*y0 + F);
-      p->a[ii*2] = x1;
-      p->a[ii*2+1] = y1;
+      GeoX(p,ii) = x1;
+      GeoY(p,ii) = y1;
     }
     sqlite3_result_blob(context, p->hdr, 
        4+8*p->nVertex, SQLITE_TRANSIENT);
@@ -477,12 +486,12 @@ static double geopolyArea(GeoPoly *p){
   double rArea = 0.0;
   int ii;
   for(ii=0; ii<p->nVertex-1; ii++){
-    rArea += (p->a[ii*2] - p->a[ii*2+2])           /* (x0 - x1) */
-              * (p->a[ii*2+1] + p->a[ii*2+3])      /* (y0 + y1) */
+    rArea += (GeoX(p,ii) - GeoX(p,ii+1))           /* (x0 - x1) */
+              * (GeoY(p,ii) + GeoY(p,ii+1))        /* (y0 + y1) */
               * 0.5;
   }
-  rArea += (p->a[ii*2] - p->a[0])                  /* (xN - x0) */
-           * (p->a[ii*2+1] + p->a[1])              /* (yN + y0) */
+  rArea += (GeoX(p,ii) - GeoX(p,0))                /* (xN - x0) */
+           * (GeoY(p,ii) + GeoY(p,0))              /* (yN + y0) */
            * 0.5;
   return rArea;
 }
@@ -529,13 +538,13 @@ static void geopolyCcwFunc(
   if( p ){
     if( geopolyArea(p)<0.0 ){
       int ii, jj;
-      for(ii=2, jj=p->nVertex*2 - 2; ii<jj; ii+=2, jj-=2){
-        GeoCoord t = p->a[ii];
-        p->a[ii] = p->a[jj];
-        p->a[jj] = t;
-        t = p->a[ii+1];
-        p->a[ii+1] = p->a[jj+1];
-        p->a[jj+1] = t;
+      for(ii=1, jj=p->nVertex-1; ii<jj; ii++, jj--){
+        GeoCoord t = GeoX(p,ii);
+        GeoX(p,ii) = GeoX(p,jj);
+        GeoX(p,jj) = t;
+        t = GeoY(p,ii);
+        GeoY(p,ii) = GeoY(p,jj);
+        GeoY(p,jj) = t;
       }
     }
     sqlite3_result_blob(context, p->hdr, 
@@ -595,8 +604,8 @@ static void geopolyRegularFunc(
   p->hdr[3] = n&0xff;
   for(i=0; i<n; i++){
     double rAngle = 2.0*GEOPOLY_PI*i/n;
-    p->a[i*2] = x - r*geopolySine(rAngle-0.5*GEOPOLY_PI);
-    p->a[i*2+1] = y + r*geopolySine(rAngle);
+    GeoX(p,i) = x - r*geopolySine(rAngle-0.5*GEOPOLY_PI);
+    GeoY(p,i) = y + r*geopolySine(rAngle);
   }
   sqlite3_result_blob(context, p->hdr, 4+8*n, SQLITE_TRANSIENT);
   sqlite3_free(p);
@@ -633,13 +642,13 @@ static GeoPoly *geopolyBBox(
   }
   if( p ){
     int ii;
-    mnX = mxX = p->a[0];
-    mnY = mxY = p->a[1];
+    mnX = mxX = GeoX(p,0);
+    mnY = mxY = GeoY(p,0);
     for(ii=1; ii<p->nVertex; ii++){
-      double r = p->a[ii*2];
+      double r = GeoX(p,ii);
       if( r<mnX ) mnX = (float)r;
       else if( r>mxX ) mxX = (float)r;
-      r = p->a[ii*2+1];
+      r = GeoY(p,ii);
       if( r<mnY ) mnY = (float)r;
       else if( r>mxY ) mxY = (float)r;
     }
@@ -659,14 +668,14 @@ static GeoPoly *geopolyBBox(
       pOut->hdr[1] = 0;
       pOut->hdr[2] = 0;
       pOut->hdr[3] = 4;
-      pOut->a[0] = mnX;
-      pOut->a[1] = mnY;
-      pOut->a[2] = mxX;
-      pOut->a[3] = mnY;
-      pOut->a[4] = mxX;
-      pOut->a[5] = mxY;
-      pOut->a[6] = mnX;
-      pOut->a[7] = mxY;
+      GeoX(pOut,0) = mnX;
+      GeoY(pOut,0) = mnY;
+      GeoX(pOut,1) = mxX;
+      GeoY(pOut,1) = mnY;
+      GeoX(pOut,2) = mxX;
+      GeoY(pOut,2) = mxY;
+      GeoX(pOut,3) = mnX;
+      GeoY(pOut,3) = mxY;
     }else{
       sqlite3_free(p);
       aCoord[0].f = mnX;
@@ -804,14 +813,14 @@ static void geopolyContainsPointFunc(
   int ii;
   if( p1==0 ) return;
   for(ii=0; ii<p1->nVertex-1; ii++){
-    v = pointBeneathLine(x0,y0,p1->a[ii*2],p1->a[ii*2+1],
-                               p1->a[ii*2+2],p1->a[ii*2+3]);
+    v = pointBeneathLine(x0,y0,GeoX(p1,ii), GeoY(p1,ii),
+                               GeoX(p1,ii+1),GeoY(p1,ii+1));
     if( v==2 ) break;
     cnt += v;
   }
   if( v!=2 ){
-    v = pointBeneathLine(x0,y0,p1->a[ii*2],p1->a[ii*2+1],
-                               p1->a[0],p1->a[1]);
+    v = pointBeneathLine(x0,y0,GeoX(p1,ii), GeoY(p1,ii),
+                               GeoX(p1,0),  GeoY(p1,0));
   }
   if( v==2 ){
     sqlite3_result_int(context, 1);
@@ -933,10 +942,10 @@ static void geopolyAddSegments(
   unsigned int i;
   GeoCoord *x;
   for(i=0; i<(unsigned)pPoly->nVertex-1; i++){
-    x = pPoly->a + (i*2);
+    x = &GeoX(pPoly,i);
     geopolyAddOneSegment(p, x[0], x[1], x[2], x[3], side, i);
   }
-  x = pPoly->a + (i*2);
+  x = &GeoX(pPoly,i);
   geopolyAddOneSegment(p, x[0], x[1], pPoly->a[0], pPoly->a[1], side, i);
 }
 
diff --git a/manifest b/manifest
index af8ade47d7..0cf7d7a966 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Fix\sproblems\scausing\sundefined\sleft-shift\soperations\sin\sthe\sfts3\ssnippet()\nfunction.
-D 2019-01-18T19:26:48.918
+C Typecasts\sadded\sto\sthe\sGeoPoly\sextension\sto\savoid\sharmless\sUBSAN\swarnings.
+D 2019-01-18T19:33:56.463
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F Makefile.in 2a9d0331ab57c68173a4c2fe9046fe89c4d916a888e04dd7a2d36958c2bff777
@@ -366,7 +366,7 @@ F ext/repair/test/checkfreelist01.test 3e8aa6aeb4007680c94a8d07b41c339aa635cc782
 F ext/repair/test/checkindex01.test b530f141413b587c9eb78ff734de6bb79bc3515c335096108c12c01bddbadcec
 F ext/repair/test/test.tcl 686d76d888dffd021f64260abf29a55c57b2cedfa7fc69150b42b1d6119aac3c
 F ext/rtree/README 6315c0d73ebf0ec40dedb5aa0e942bc8b54e3761
-F ext/rtree/geopoly.c 603ec9b72cd70cf18541339b6c7d47f304ac0d84c50294be6c6c6ae35acdb0a6
+F ext/rtree/geopoly.c 061432bddc38c4c10c7e4ce940d581c886d65bb5814b4b65b46ad046aa85eaa2
 F ext/rtree/rtree.c 57729cc19f3832e5f9051556af44ed264b5bd54b01543cd7e50d5143817b964c
 F ext/rtree/rtree.h 4a690463901cb5e6127cf05eb8e642f127012fd5003830dbc974eca5802d9412
 F ext/rtree/rtree1.test 7573134f1b4f59df36c1b0a6de51268fd3b9c714d91f3811482263e734e416ea
@@ -1800,7 +1800,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P b352f1590d20a574b0681e011ececcf4f41fa5b157503d330e03939404aca0e9
-R cf317d4e595abdb01b27661d8f9d1df1
-U dan
-Z 1d119c13c18ffa9046c8d95a13a2ae82
+P b90dbaed3092236e97f9796fa63989a3648060e16189e1267c430f4a7e799fac
+R 38e7ed21c3ba7e18d21fd38b5b228c8f
+U drh
+Z 71c939a2336f695a4bb7bcd852576d14
diff --git a/manifest.uuid b/manifest.uuid
index 8a56f6fdf9..2ebe496726 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-b90dbaed3092236e97f9796fa63989a3648060e16189e1267c430f4a7e799fac
\ No newline at end of file
+a1f6a093ac4a2de8c5b02c30fe57e09770460fd5bdddfe9c7a9a24fb83a6b491
\ No newline at end of file