In a wireless network supporting aggregation of uplink component carriers, sounding reference signals, SRS, are transmitted on an uplink, UL, primary component carrier. An activation command corresponding to an UL secondary component carrier, SCC, is received, in response to which the receiving transceiver determines whether it has valid timing information for the UL SCC, wherein valid timing information for the UL SCC indicates that the UL SCC is UL synchronized. In response to this determination, transmission of SRS on the UL SCC is enabled if the UL SCC is synchronized, when SRS is configured for the UL SCC. Otherwise, transmission of SRS on the UL SCC is prohibited until the UL SCC is UL synchronized.