A magnetic-inductive flowmeter for measuring the flow of a conductive medium having a measuring tube, a magnetic field generator, a magnetic circuit device for guiding the measuring magnetic field, electrodes for detecting a flow-dependent electrical measuring voltage when the conductive medium flows through the measuring tube, and an electronic control and evaluation unit, and a method for operating the magnetic-inductive flowmeter. To make the magnetic-inductive flowmeter which smaller and cheaper, a sensor for detecting a physical disturbance variable acting on the magnetic circuit device is arranged on the magnetic circuit device, wherein the measuring magnetic field is influenced by the physical disturbance variable and wherein the control and evaluation unit is designed such that it detects and signals an exceeding or falling below of a pre-definable limit value of the physical disturbance variable and/or performs a correction of the effect of the physical disturbance variable on the flow measurement.