diff --git a/libsharp/sharp_ylmgen_c.c b/libsharp/sharp_ylmgen_c.c
index 5f0f1a1..1baa2c8 100644
--- a/libsharp/sharp_ylmgen_c.c
+++ b/libsharp/sharp_ylmgen_c.c
@@ -47,7 +47,9 @@ void sharp_Ylmgen_init (sharp_Ylmgen_C *gen, int l_max, int m_max, int spin)
 
   gen->lmax = l_max;
   gen->mmax = m_max;
-  UTIL_ASSERT(spin>=0,"incorrect spin");
+  UTIL_ASSERT(spin>=0,"incorrect spin: must be nonnegative");
+  UTIL_ASSERT(m_max>=spin,"incorrect m_max: must be >= spin");
+  UTIL_ASSERT(l_max>=m_max,"incorrect l_max: must be >= m_max");
   gen->s = spin;
   UTIL_ASSERT((sharp_minscale<=0)&&(sharp_maxscale>0),
     "bad value for min/maxscale");