diff --git a/cmake/FindGreenplum.cmake b/cmake/FindGreenplum.cmake
index 8e064ec2f..ffed615e5 100644
--- a/cmake/FindGreenplum.cmake
+++ b/cmake/FindGreenplum.cmake
@@ -85,6 +85,7 @@ if(GREENPLUM_PG_CONFIG AND GREENPLUM_CLIENT_INCLUDE_DIR)
     else(GREENPLUM_PACKAGE_NAME STREQUAL "Greenplum Database")
         message(STATUS "Found pg_config at \"${GREENPLUM_PG_CONFIG}\", but it does not point to a Greenplum installation.")
         unset(GREENPLUM_CLIENT_INCLUDE_DIR)
+        unset(GREENPLUM_VERSION_STRING)
     endif(GREENPLUM_PACKAGE_NAME STREQUAL "Greenplum Database")
 endif(GREENPLUM_PG_CONFIG AND GREENPLUM_CLIENT_INCLUDE_DIR)
 
diff --git a/cmake/FindPostgreSQL.cmake b/cmake/FindPostgreSQL.cmake
index 1515161e4..5336968d7 100644
--- a/cmake/FindPostgreSQL.cmake
+++ b/cmake/FindPostgreSQL.cmake
@@ -80,6 +80,7 @@ if(POSTGRESQL_PG_CONFIG AND POSTGRESQL_CLIENT_INCLUDE_DIR)
         # here.
         message(STATUS "Found pg_config at \"${POSTGRESQL_PG_CONFIG}\", but it does not point to a PostgreSQL installation.")
         unset(POSTGRESQL_CLIENT_INCLUDE_DIR)
+        unset(POSTGRESQL_VERSION_STRING)
     endif(POSTGRESQL_PACKAGE_NAME STREQUAL "PostgreSQL")
 endif(POSTGRESQL_PG_CONFIG AND POSTGRESQL_CLIENT_INCLUDE_DIR)