Refractive and diffractive scintillation are thought to be two related effects of scattering in the interstellar medium. The predicted modulation of diffractive scintillation parameters by refractive effects has not been thoroughly tested, however. We report 24 days of scintillation observations of the radio pulsar PSR B0329+54 from September 1993 to June 1994 with a 26-m telescope operating at 610 MHz. Dynamic spectra were obtained on each day, from which the characteristic bandwidth and time scale of the diffractive scintillation pattern were determined. A relative flux value for the pulsar was also obtained on each day. The cross-correlation coefficient for each unique pair of the observables — flux, δF, bandwidth, δν and time scale, δt — was formed from these data. The observed values of these coefficients and their 67% confidenceintervals are: CδFδν = −0.4 ± 0.2, CδFδt = −0.7 ± 0.1, and Cδνδt = 0.5 ± 0.2. Theoretical expectations are that CδFδν = −0.8, CδFδt = −0.6, and Cδνδt = 0.8. We conclude that we have detected the expected modulation of diffractive parameters by refractive scintillation. This adds confidence to the interpretation that diffractive and refractive scintillation of compact radio sources are caused by the same underlying scattering process.