diff --git a/ext/session/sessionD.test b/ext/session/sessionD.test
index aab9fdaea8..6fc47075d5 100644
--- a/ext/session/sessionD.test
+++ b/ext/session/sessionD.test
@@ -184,5 +184,36 @@ do_execsql_test 3.0 {
 }
 do_empty_diff_test 3.1
 
+
+#-------------------------------------------------------------------------
+# Test some error cases:
+# 
+#   1) schema mismatches between the two dbs, and 
+#   2) tables with no primary keys.
+#
+reset_db
+forcedelete test.db2
+do_execsql_test 4.0 {
+  ATTACH 'test.db2' AS ixua;
+  CREATE TABLE ixua.t1(a, b, c);
+  CREATE TABLE main.t1(a, b, c);
+
+  CREATE TABLE ixua.t2(a PRIMARY KEY, b, c);
+  CREATE TABLE main.t2(a PRIMARY KEY, b, x);
+}
+
+do_test 4.1 {
+  sqlite3session S db main
+  S attach t1
+  list [catch { S diff ixua t1 } msg] $msg
+} {1 {table has no primary key}}
+
+do_test 4.2 {
+  S attach t2
+  list [catch { S diff ixua t2 } msg] $msg
+} {1 {table schemas do not match}}
+
+S delete
+
 finish_test
 
diff --git a/ext/session/sqlite3session.c b/ext/session/sqlite3session.c
index 70bd250e34..f5a6096611 100644
--- a/ext/session/sqlite3session.c
+++ b/ext/session/sqlite3session.c
@@ -1473,18 +1473,21 @@ int sqlite3session_diff(
 
     /* Check the table schemas match */
     if( rc==SQLITE_OK ){
+      int bHasPk = 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 || memcmp(pTo->abPK, abPK, nCol) ){
+        if( pTo->nCol!=nCol ){
           bMismatch = 1;
         }else{
           int i;
           for(i=0; i<nCol; i++){
+            if( pTo->abPK[i]!=abPK[i] ) bMismatch = 1;
             if( sqlite3_stricmp(azCol[i], pTo->azCol[i]) ) bMismatch = 1;
+            if( abPK[i] ) bHasPk = 1;
           }
         }
 
@@ -1492,6 +1495,10 @@ int sqlite3session_diff(
           *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);
     }
diff --git a/ext/session/test_session.c b/ext/session/test_session.c
index 3dc24fc69e..b3f2533ff5 100644
--- a/ext/session/test_session.c
+++ b/ext/session/test_session.c
@@ -228,6 +228,7 @@ static int test_session_cmd(
       assert( rc!=SQLITE_OK || zErr==0 );
       if( zErr ){
         Tcl_AppendResult(interp, zErr, 0);
+        sqlite3_free(zErr);
         return TCL_ERROR;
       }
       if( rc ){
diff --git a/manifest b/manifest
index d6c7250535..5b54ca3c2e 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Fix\sa\sperformance\sproblem\sin\ssqlite3session_diff().
-D 2015-04-23T14:40:17.627
+C Fix\sthe\serror\smessage\sreturned\sby\ssqlite3session_diff()\sfor\stables\swith\sno\sPRIMARY\sKEY.
+D 2015-04-23T15:03:14.997
 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 197781b4823fbf0003a21da0e4360b37d0e0a81f
+F ext/session/sessionD.test bdc20e2384bf92b5719b9e41ad3b18cd9188cf26
 F ext/session/session_common.tcl 9de0451b6a47218fc16b9ed8876b6238a0a3d88d
 F ext/session/sessionfault.test bef044d0952c0d62c31c8d2400be72c8684545cc
-F ext/session/sqlite3session.c de11ba62d7bf5b9a5d732411550771d4ee6b412a
+F ext/session/sqlite3session.c 0b26c45c0c3c0b2afaae9bd69ae1e80a6b8e9b5a
 F ext/session/sqlite3session.h d9ebd8d4c5791aafdf18165575c7f2223c09279b
-F ext/session/test_session.c 037fc25340a918eb2195972fed439d7adf7b5db9
+F ext/session/test_session.c 67a049635d910c55917f23d067575ab5432d4546
 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 4e5f17d189eb0578a544c21fc150f9e2ee3428e3
-R bb0c0c482394af2863743ccd1d1a9362
+P ea400eca314d81761fe5c0e329b906c045f0dfe4
+R 57c462c26b9985ec1f9daf86d6b971a1
 U dan
-Z ee0bd6bc3557d1b9872d331b62e53091
+Z dd15ced7dcdddbd36a44e0c8439b0673
diff --git a/manifest.uuid b/manifest.uuid
index e79db0245b..9d7404abb8 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-ea400eca314d81761fe5c0e329b906c045f0dfe4
\ No newline at end of file
+4d34a3d40da210bebb2a2e6dff094f9a39c92798
\ No newline at end of file