diff --git a/LOG b/LOG
index a4ed4474fd..6b73a069ec 100644
--- a/LOG
+++ b/LOG
@@ -999,3 +999,5 @@
     misc.ms
 - flush expand-output and expand/optimize-output ports
     compile.ss
+- clarify "unknown module" error message in determine-module-imports
+    syntax.ss
diff --git a/s/syntax.ss b/s/syntax.ss
index 119c6e51a7..a20e5c89b6 100644
--- a/s/syntax.ss
+++ b/s/syntax.ss
@@ -4071,7 +4071,7 @@
      ;     (and <sub-version ref>*)
      ;     (or <sub-version ref>*)
      ;     (not <sub-version ref>)
-      (define (determine-module-imports what mid tid)
+      (define (determine-module-imports what who mid tid)
         (let ([binding (lookup (id->label mid empty-wrap) r)])
           (case (binding-type binding)
             [($module)
@@ -4087,7 +4087,7 @@
                (values mid tid
                  (make-import-interface x
                    (diff-marks (id-marks tid) (interface-marks (get-indirect-interface x))))))]
-            [else (syntax-error mid "unknown module")])))
+            [else (syntax-error who (format "unknown ~a" what))])))
       (define (impset x)
         (syntax-case x ()
           [(?only *x id ...)
@@ -4222,13 +4222,13 @@
                              [else (f (cdr imps) o.n* (cons a new-imps))]))))))))]
           [mid
            (and (not std?) (id? #'mid))
-           (determine-module-imports "module" #'mid #'mid)]
+           (determine-module-imports "module" #'mid #'mid #'mid)]
           [(?library-reference lr)
            (sym-kwd? ?library-reference library-reference)
            (let-values ([(mid tid) (lookup-library #'lr)])
-             (determine-module-imports "library" mid tid))]
+             (determine-module-imports "library" #'lr mid tid))]
           [lr (let-values ([(mid tid) (lookup-library #'lr)])
-                (determine-module-imports "library" mid tid))]))
+                (determine-module-imports "library" #'lr mid tid))]))
       (syntax-case impspec (for)
         [(?for *x level ...)
          (sym-kwd? ?for for)