diff --git a/ext/session/sessionD.test b/ext/session/sessionD.test
index 6fc47075d5..b8572782e2 100644
--- a/ext/session/sessionD.test
+++ b/ext/session/sessionD.test
@@ -189,7 +189,8 @@ do_empty_diff_test 3.1
 # Test some error cases:
 # 
 #   1) schema mismatches between the two dbs, and 
-#   2) tables with no primary keys.
+#   2) tables with no primary keys. This is not actually an error, but
+#      should not add any changes to the session object.
 #
 reset_db
 forcedelete test.db2
@@ -197,22 +198,27 @@ do_execsql_test 4.0 {
   ATTACH 'test.db2' AS ixua;
   CREATE TABLE ixua.t1(a, b, c);
   CREATE TABLE main.t1(a, b, c);
+  INSERT INTO main.t1 VALUES(1, 2, 3);
 
   CREATE TABLE ixua.t2(a PRIMARY KEY, b, c);
   CREATE TABLE main.t2(a PRIMARY KEY, b, x);
 }
 
-do_test 4.1 {
+do_test 4.1.1 {
   sqlite3session S db main
   S attach t1
   list [catch { S diff ixua t1 } msg] $msg
-} {1 {table has no primary key}}
+} {0 {}}
+do_test 4.1.2 {
+  string length [S changeset]
+} {0}
+S delete
 
-do_test 4.2 {
+do_test 4.2.2 {
+  sqlite3session S db main
   S attach t2
   list [catch { S diff ixua t2 } msg] $msg
-} {1 {table schemas do not match}}
-
+} {1 {SQLITE_SCHEMA - table schemas do not match}}
 S delete
 
 finish_test
diff --git a/ext/session/sqlite3session.c b/ext/session/sqlite3session.c
index f5a6096611..b5a1b9dfa3 100644
--- a/ext/session/sqlite3session.c
+++ b/ext/session/sqlite3session.c
@@ -1474,12 +1474,12 @@ int sqlite3session_diff(
     /* Check the table schemas match */
     if( rc==SQLITE_OK ){
       int bHasPk = 0;
+      int bMismatch = 0;
       int nCol;                   /* Columns in zFrom.zTbl */
       u8 *abPK;
       const char **azCol = 0;
       rc = sessionTableInfo(db, zFrom, zTbl, &nCol, 0, &azCol, &abPK);
       if( rc==SQLITE_OK ){
-        int bMismatch = 0;
         if( pTo->nCol!=nCol ){
           bMismatch = 1;
         }else{
@@ -1491,16 +1491,16 @@ int sqlite3session_diff(
           }
         }
 
-        if( bMismatch ){
-          *pzErrMsg = sqlite3_mprintf("table schemas do not match");
-          rc = SQLITE_ERROR;
-        }
-        if( bHasPk==0 ){
-          *pzErrMsg = sqlite3_mprintf("table has no primary key");
-          rc = SQLITE_ERROR;
-        }
       }
       sqlite3_free(azCol);
+      if( bMismatch ){
+        *pzErrMsg = sqlite3_mprintf("table schemas do not match");
+        rc = SQLITE_SCHEMA;
+      }
+      if( bHasPk==0 ){
+        /* Ignore tables with no primary keys */
+        goto diff_out;
+      }
     }
 
     if( rc==SQLITE_OK ){
diff --git a/ext/session/sqlite3session.h b/ext/session/sqlite3session.h
index ed1c5d917c..c8ce488ba7 100644
--- a/ext/session/sqlite3session.h
+++ b/ext/session/sqlite3session.h
@@ -293,6 +293,11 @@ int sqlite3session_changeset(
 **   <li> Has the same PRIMARY KEY definition.
 ** </ul>
 **
+** If the tables are not compatible, SQLITE_SCHEMA is returned. If the tables
+** are compatible but do not have any PRIMARY KEY columns, it is not an error
+** but no changes are added to the session object. As with other session
+** APIs, tables without PRIMARY KEYs are simply ignored.
+**
 ** This function adds a set of changes to the session object that could be
 ** used to update the table in database zFrom (call this the "from-table") 
 ** so that its content is the same as the table attached to the session 
diff --git a/ext/session/test_session.c b/ext/session/test_session.c
index b3f2533ff5..15f7b6f575 100644
--- a/ext/session/test_session.c
+++ b/ext/session/test_session.c
@@ -39,9 +39,13 @@ static int test_tcl_integer(Tcl_Interp *interp, const char *zVar){
   return iVal;
 }
 
-static int test_session_error(Tcl_Interp *interp, int rc){
+static int test_session_error(Tcl_Interp *interp, int rc, char *zErr){
   extern const char *sqlite3ErrName(int);
   Tcl_SetObjResult(interp, Tcl_NewStringObj(sqlite3ErrName(rc), -1));
+  if( zErr ){
+    Tcl_AppendResult(interp, " - ", zErr, 0);
+    sqlite3_free(zErr);
+  }
   return TCL_ERROR;
 }
 
@@ -150,7 +154,7 @@ static int test_session_cmd(
       if( zArg[0]=='*' && zArg[1]=='\0' ) zArg = 0;
       rc = sqlite3session_attach(pSession, zArg);
       if( rc!=SQLITE_OK ){
-        return test_session_error(interp, rc);
+        return test_session_error(interp, rc, 0);
       }
       break;
     }
@@ -177,7 +181,7 @@ static int test_session_cmd(
       }
       sqlite3_free(o.p);
       if( rc!=SQLITE_OK ){
-        return test_session_error(interp, rc);
+        return test_session_error(interp, rc, 0);
       }
       break;
     }
@@ -226,13 +230,8 @@ static int test_session_cmd(
           &zErr
       );
       assert( rc!=SQLITE_OK || zErr==0 );
-      if( zErr ){
-        Tcl_AppendResult(interp, zErr, 0);
-        sqlite3_free(zErr);
-        return TCL_ERROR;
-      }
       if( rc ){
-        return test_session_error(interp, rc);
+        return test_session_error(interp, rc, zErr);
       }
       break;
     }
@@ -278,7 +277,7 @@ static int test_sqlite3session(
   rc = sqlite3session_create(db, Tcl_GetString(objv[3]), &p->pSession);
   if( rc!=SQLITE_OK ){
     ckfree((char*)p);
-    return test_session_error(interp, rc);
+    return test_session_error(interp, rc, 0);
   }
 
   Tcl_CreateObjCommand(
@@ -652,7 +651,7 @@ static int test_sqlite3changeset_apply(
   }
 
   if( rc!=SQLITE_OK ){
-    return test_session_error(interp, rc);
+    return test_session_error(interp, rc, 0);
   }
   Tcl_ResetResult(interp);
   return TCL_OK;
@@ -686,7 +685,7 @@ static int test_sqlite3changeset_apply_replace_all(
 
   rc = sqlite3changeset_apply(db, nChangeset, pChangeset, 0, replace_handler,0);
   if( rc!=SQLITE_OK ){
-    return test_session_error(interp, rc);
+    return test_session_error(interp, rc, 0);
   }
   Tcl_ResetResult(interp);
   return TCL_OK;
@@ -724,7 +723,7 @@ static int test_sqlite3changeset_invert(
     rc = sqlite3changeset_invert(sIn.nData, sIn.aData, &sOut.n, &sOut.p);
   }
   if( rc!=SQLITE_OK ){
-    rc = test_session_error(interp, rc);
+    rc = test_session_error(interp, rc, 0);
   }else{
     Tcl_SetObjResult(interp,Tcl_NewByteArrayObj((unsigned char*)sOut.p,sOut.n));
   }
@@ -772,7 +771,7 @@ static int test_sqlite3changeset_concat(
   }
 
   if( rc!=SQLITE_OK ){
-    rc = test_session_error(interp, rc);
+    rc = test_session_error(interp, rc, 0);
   }else{
     Tcl_SetObjResult(interp,Tcl_NewByteArrayObj((unsigned char*)sOut.p,sOut.n));
   }
@@ -824,7 +823,7 @@ static int test_sqlite3session_foreach(
     rc = sqlite3changeset_start_strm(&pIter, testStreamInput, (void*)&sStr);
   }
   if( rc!=SQLITE_OK ){
-    return test_session_error(interp, rc);
+    return test_session_error(interp, rc, 0);
   }
 
   while( SQLITE_ROW==sqlite3changeset_next(pIter) ){
@@ -907,7 +906,7 @@ static int test_sqlite3session_foreach(
     rc = sqlite3changeset_finalize(pIter);
   }
   if( rc!=SQLITE_OK ){
-    return test_session_error(interp, rc);
+    return test_session_error(interp, rc, 0);
   }
 
   return TCL_OK;
diff --git a/manifest b/manifest
index 5b54ca3c2e..cc09519aa2 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Fix\sthe\serror\smessage\sreturned\sby\ssqlite3session_diff()\sfor\stables\swith\sno\sPRIMARY\sKEY.
-D 2015-04-23T15:03:14.997
+C Modify\sthe\ssqlite3session_diff()\sAPI\sso\sthat\stables\swith\sno\sPRIMARY\sKEYs\sare\signored.\sThis\smatches\sthe\sother\ssessions\sAPIs.\sAlso\schange\ssqlite3session_diff()\sso\sthat\sit\sreturns\sSQLITE_SCHEMA,\sinstead\sof\sSQLITE_ERROR,\sif\sthe\stables\sbeing\scompared\sdo\snot\shave\scompatible\sschemas.
+D 2015-04-23T17:22:50.000
 F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
 F Makefile.in 7599f0c96df628cd543884b1b2f2a2fbffd00079
 F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@ -158,12 +158,12 @@ F ext/session/session9.test 5409d90d8141881d08285ed1c2c0d8d10fb92069
 F ext/session/sessionA.test 1feeab0b8e03527f08f2f1defb442da25480138f
 F ext/session/sessionB.test 06961b7c3641151f5d23088250ecad132501113c
 F ext/session/sessionC.test 3982f8577b0744c5ce3aaef7cfeb5bd903f17fe4
-F ext/session/sessionD.test bdc20e2384bf92b5719b9e41ad3b18cd9188cf26
+F ext/session/sessionD.test d4744c78334162851d2a2f285c7e603e31b49aa2
 F ext/session/session_common.tcl 9de0451b6a47218fc16b9ed8876b6238a0a3d88d
 F ext/session/sessionfault.test bef044d0952c0d62c31c8d2400be72c8684545cc
-F ext/session/sqlite3session.c 0b26c45c0c3c0b2afaae9bd69ae1e80a6b8e9b5a
-F ext/session/sqlite3session.h d9ebd8d4c5791aafdf18165575c7f2223c09279b
-F ext/session/test_session.c 67a049635d910c55917f23d067575ab5432d4546
+F ext/session/sqlite3session.c d22a8996f44202a13d0b1ad18757cd509729a23c
+F ext/session/sqlite3session.h 8e86f9eec3ed71f1f30eefbe810cbe5bc10b5aa9
+F ext/session/test_session.c 187bd344c5ae9d5be85e22ef7c3010f0c17307ce
 F ext/userauth/sqlite3userauth.h 19cb6f0e31316d0ee4afdfb7a85ef9da3333a220
 F ext/userauth/user-auth.txt e6641021a9210364665fe625d067617d03f27b04
 F ext/userauth/userauth.c 5fa3bdb492f481bbc1709fc83c91ebd13460c69e
@@ -1271,7 +1271,7 @@ F tool/vdbe_profile.tcl 67746953071a9f8f2f668b73fe899074e2c6d8c1
 F tool/warnings-clang.sh f6aa929dc20ef1f856af04a730772f59283631d4
 F tool/warnings.sh 0abfd78ceb09b7f7c27c688c8e3fe93268a13b32
 F tool/win/sqlite.vsix deb315d026cc8400325c5863eef847784a219a2f
-P ea400eca314d81761fe5c0e329b906c045f0dfe4
-R 57c462c26b9985ec1f9daf86d6b971a1
+P 4d34a3d40da210bebb2a2e6dff094f9a39c92798
+R 77fdc1b8d856af82047ddfafb467bba9
 U dan
-Z dd15ced7dcdddbd36a44e0c8439b0673
+Z c001be8d13359c151923937b5aa6a277
diff --git a/manifest.uuid b/manifest.uuid
index 9d7404abb8..ef8da808c5 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-4d34a3d40da210bebb2a2e6dff094f9a39c92798
\ No newline at end of file
+aada0ad08e3baa10d14d1f3393183110289e068e
\ No newline at end of file