diff --git a/src/secp256k1/src/scalar_impl.h b/src/secp256k1/src/scalar_impl.h
--- a/src/secp256k1/src/scalar_impl.h
+++ b/src/secp256k1/src/scalar_impl.h
@@ -254,6 +254,14 @@
 
 #ifdef USE_ENDOMORPHISM
 #if defined(EXHAUSTIVE_TEST_ORDER)
+#  if EXHAUSTIVE_TEST_ORDER == 13
+#    define EXHAUSTIVE_TEST_LAMBDA 9
+#  elif EXHAUSTIVE_TEST_ORDER == 199
+#    define EXHAUSTIVE_TEST_LAMBDA 92
+#  else
+#    error No known lambda for the specified exhaustive test group order.
+#  endif
+
 /**
  * Find k1 and k2 given k, such that k1 + k2 * lambda == k mod n; unlike in the
  * full case we don't bother making k1 and k2 be small, we just want them to be
diff --git a/src/secp256k1/src/tests_exhaustive.c b/src/secp256k1/src/tests_exhaustive.c
--- a/src/secp256k1/src/tests_exhaustive.c
+++ b/src/secp256k1/src/tests_exhaustive.c
@@ -18,7 +18,6 @@
 #ifndef EXHAUSTIVE_TEST_ORDER
 /* see group_impl.h for allowable values */
 #define EXHAUSTIVE_TEST_ORDER 13
-#define EXHAUSTIVE_TEST_LAMBDA 9   /* cube root of 1 mod 13 */
 #endif
 
 #include "include/secp256k1.h"