We conducted an experimental investigation of the structural and magnetic properties of Al-Mn-doped ZrO2 and ZnO thin films. It was found that, even though additional Al doping does not substantially enhance ferromagnetism (FM), it influences surface magnetism by enhancing it. Increase of the Al concentration slightly improves the overall magnetization of the Al-Mn-doped ZrO2 sample, however, this effect is also accompanied by a deterioration of the crystallinity of the sample. On the other hand, we found that by co-doping the Mn-doped ZnO samples with Al, the result is a significant increase of the magnetic moment. Apart from the surface effects, the data clearly indicate that the observed FM originates from defects. Our results confirm that co-doping with Al can be an efficient way to enhance magnetism and control the distribution of defects for certain transition-metal-doped semiconducting oxides.