Strong constraints on thirteenth-order terms in the geopotential have been derived from U.S. Navy tracking on a Diademe 2 fragment (1967-14F). This object (perigee height, 580km; orbit inclination, 38.9¿) has recently decayed slowly through the perfect commensurability with these terms. The resonance forces have increased its inclination by 0.03¿. The principal constraint (in fully normalized harmonics), derived by adjustment of a pair of harmonic coefficients to the Navy inclination data (mainly), is 109(10.5¿1.8, 50.8¿1.0) =0.023(C, S)13,13 -0.172(C, S)15,13+0.505(C, S)17,13-0.884(C, S)19,13+(C, S)21,13-0.673(C, S)23,13+0.099(C, S)25,13+0.295(C,S)27,13-0.279(C, S29,13+0.018(C, S)31,13+⋅⋅⋅. Recent geopotential solutions for thirteenth-order terms, which include Diademe 2 (satellite) data, are up to 25% in error (as a set) when they are judged by this independent tracking information.