diff --git a/s/priminfo.ss b/s/priminfo.ss
index 628536927e..db403f3cf0 100644
--- a/s/priminfo.ss
+++ b/s/priminfo.ss
@@ -14,7 +14,7 @@
 ;;; limitations under the License.
 
 (module priminfo (priminfo-unprefixed priminfo-libraries priminfo-mask priminfo-signatures priminfo-arity primvec
-                  get-priminfo priminfo-boolean? priminfo-result-arity)
+                  get-priminfo priminfo-boolean? priminfo-true? priminfo-result-arity)
   (define-record-type priminfo
     (nongenerative)
     (sealed #t)
@@ -55,6 +55,28 @@
           'single]
          [else 'multiple]))))
 
+  (define priminfo-true?
+    (lambda (info)
+      (let ([signature* (priminfo-signatures info)])
+        (cond
+         [(null? signature*) 'unknown]
+         [(andmap (lambda (sig)
+                    (let ([out (cdr sig)])
+                      (and (pair? out)
+                           (null? (cdr out))
+                           (or (pair? (car out))
+                           (not (or (eq? (car out) 'ptr)
+                                    (eq? (car out) 'sub-ptr)
+                                    (eq? (car out) 'boolean)
+                                    (eq? (car out) 'bottom)
+                                    (eq? (car out) 'who)
+                                    (let ([name (symbol->string (car out))])
+                                      (and (>= (string-length name) 6)
+                                           (string=? (substring name 0 6) "maybe-"))))))))) 
+                  signature*)
+          'true]
+         [else #;(newline) #;(display (list info)) 'other]))))
+
   (define signature->interface
     (lambda (sig)
       (define (ellipsis? x) (eq? x '...))
diff --git a/s/primvars.ss b/s/primvars.ss
index 8dc5154da0..677971ae6b 100644
--- a/s/primvars.ss
+++ b/s/primvars.ss
@@ -18,10 +18,11 @@
   (include "primref.ss")
 
   (define record-prim!
-    (lambda (prim unprefixed flags arity boolean-valued? result-arity signatures)
+    (lambda (prim unprefixed flags arity boolean-valued? true-valued? result-arity signatures)
       (unless (eq? unprefixed prim) ($sputprop prim '*unprefixed* unprefixed))
       (let* ([flags (if boolean-valued? (fxlogor flags (prim-mask boolean-valued)) flags)]
              [flags (if (eq? 'single result-arity) (fxlogor flags (prim-mask single-valued)) flags)]
+             [flags (if (eq? 'true true-valued?) (fxlogor flags (prim-mask true)) flags)]
              [arity (and (not (null? arity)) arity)])
         (when (and (eq? result-arity 'multiple) (any-set? (prim-mask single-valued) flags))
           ($oops 'prims "inconsistent single-value information for ~s" prim))
@@ -42,6 +43,7 @@
               '#,(datum->syntax #'* (vector-map priminfo-mask v-info))
               '#,(datum->syntax #'* (vector-map priminfo-arity v-info))
               '#,(datum->syntax #'* (vector-map priminfo-boolean? v-info))
+              '#,(datum->syntax #'* (vector-map priminfo-true? v-info))
               '#,(datum->syntax #'* (vector-map priminfo-result-arity v-info))
               '#,(datum->syntax #'* (vector-map priminfo-signatures v-info)))))))