Day and Bamford's ten principles for promoting second-language (L2) extensive reading (ER) have been commended for their highly applicable practicality. However, for various reasons, assuring successful ER instruction can remain a challenging task. This surprising contrast may in part be clarified by examining the relationship between Day and Bamford's recommendations and the factors highlighted in the Self-Determination Theory (SDT) of motivation. Day and Bamford's ten recommendations incorporate features that can be viewed as exemplifying one or more of the three SDT components--competence, autonomy, and relatedness--which, SDT argues, should all be present in an ideally motivational environment. However, a mixed-method study of 9 adult ESL instructors (Likert scale questionnaires, plus follow-up interviews) suggested that selective adherence to some but not all dimensions of Day and Bamford's guidance may allow SDT constituents to be unwittingly underrepresented. We therefore advise that Day and Bamford's principles for ER instruction should be explicitly associated with the SDT framework, in order to draw practitioners' attention as directly as possible to the full range of motivational resources available. Implications are proposed for pre-service teacher education, institutional planning, and in-service professional development.