diff --git a/ChangeLog b/ChangeLog
index e9881c9c..7f5ddbb2 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,8 @@
 2007-05-29  Federico Di Gregorio  <fog@initd.org>
 
+	* Applied patch from mkz (ticket #187) to add error handling when calling
+	conn_commit() and conn_rollback(). Fixes #187.
+
 	* cursor.copy_expert() implementation by David Rushby (copy_expert set 5/5.)
 
 	* SQL validation refactor patch from David Rushby (copy_expert set 4/5.)
diff --git a/psycopg/connection_type.c b/psycopg/connection_type.c
index ae737b57..4eb16805 100644
--- a/psycopg/connection_type.c
+++ b/psycopg/connection_type.c
@@ -117,8 +117,11 @@ psyco_conn_commit(connectionObject *self, PyObject *args)
 
     if (!PyArg_ParseTuple(args, "")) return NULL;
 
-    /* FIXME: check return status? */
-    conn_commit(self);
+    if (conn_commit(self) < 0) {
+        PyErr_SetString(OperationalError,
+                        PQerrorMessage(self->pgconn));
+        return NULL;
+    }
 
     Py_INCREF(Py_None);
     return Py_None;
@@ -137,8 +140,11 @@ psyco_conn_rollback(connectionObject *self, PyObject *args)
 
     if (!PyArg_ParseTuple(args, "")) return NULL;
 
-    /* FIXME: check return status? */
-    conn_rollback(self);
+    if (conn_rollback(self) < 0) {
+        PyErr_SetString(OperationalError,
+                        PQerrorMessage(self->pgconn));
+        return NULL;
+    }
 
     Py_INCREF(Py_None);
     return Py_None;
@@ -167,8 +173,12 @@ psyco_conn_set_isolation_level(connectionObject *self, PyObject *args)
         return NULL;
     }
 
-    /* FIXME: check return status? */
-    conn_switch_isolation_level(self, level);
+    if (conn_switch_isolation_level(self, level) < 0) {
+        PyErr_SetString(OperationalError,
+                        PQerrorMessage(self->pgconn));
+        return NULL;
+    }
+
 
     Py_INCREF(Py_None);
     return Py_None;
diff --git a/psycopg/pqpath.c b/psycopg/pqpath.c
index 28cdde80..c568c694 100644
--- a/psycopg/pqpath.c
+++ b/psycopg/pqpath.c
@@ -397,13 +397,29 @@ pq_execute(cursorObject *curs, const char *query, int async)
     Py_BEGIN_ALLOW_THREADS;
     pthread_mutex_lock(&(curs->conn->lock));
 
-    pq_begin(curs->conn);
+    if (pq_begin(curs->conn) < 0) {
+        pthread_mutex_unlock(&(curs->conn->lock));
+        Py_BLOCK_THREADS;
+        PyErr_SetString(OperationalError,
+                        PQerrorMessage(curs->conn->pgconn));
+        return -1;
+    }
 
     if (async == 0) {
         IFCLEARPGRES(curs->pgres);
         Dprintf("pq_execute: executing SYNC query:");
         Dprintf("    %-.200s", query);
         curs->pgres = PQexec(curs->conn->pgconn, query);
+
+        /* dont let pgres = NULL go to pq_fetch() */
+        /* if (curs->pgres == NULL) {
+            pthread_mutex_unlock(&(curs->conn->lock));
+            Py_BLOCK_THREADS;
+            PyErr_SetString(OperationalError,
+                            PQerrorMessage(curs->conn->pgconn));
+            return -1;
+        }
+        */
     }
 
     else if (async == 1) {