Memset warning treated as error, based on its thrd argument

Question

When built without AM_CXXFLAGS += -Wno-memset-elt-size on the AutoMake Makefile, i get this error:

error: ‘memset’ used with length equal to number of elements without multiplication by element size [-Werror=memset-elt-size] memset (_floatOptions, 0, sizeof(_floatOptions));

This is the line that triggers it: memset (_floatOptions, 0, sizeof(_floatOptions));

And this is the relevant code:

class random_class
{
  public:
    enum FloatOption
    {
        numFloatOptions
    };
    
    /// Set a float option value
    /// @param f Float Option
    /// @param value value to be set
    void setFloatValue(FloatOption f, double value)
    {
        _floatOptions[f] = value; 
        _isSetFloat[f] = true;
    }

    /// Return value of an float option
    /// @param f Float Option
    /// @return HostPlacement
    double getFloatValue(FloatOption f) const
    {
        return _floatOptions[f];
    }

  private:
    double  _floatOptions[numFloatOptions];

Does anyone know why this happens and how I can mitigate it?

I couldn't find much info on this warning/error online.