diff --git a/include/mcl/bn.hpp b/include/mcl/bn.hpp
index c8255aa..4951138 100644
--- a/include/mcl/bn.hpp
+++ b/include/mcl/bn.hpp
@@ -1616,6 +1616,10 @@ inline void makeAdjP(G1& adjP, const G1& P)
 */
 inline void finalExp(Fp12& y, const Fp12& x)
 {
+	if (x.isZero()) {
+		y.clear();
+		return;
+	}
 #if 1
 	mapToCyclotomic(y, x);
 #else
diff --git a/include/mcl/fp.hpp b/include/mcl/fp.hpp
index a223317..ca32888 100644
--- a/include/mcl/fp.hpp
+++ b/include/mcl/fp.hpp
@@ -531,7 +531,11 @@ public:
 		if (mulSmallUnit(z, x, y)) return;
 		op_.fp_mulUnit(z.v_, x.v_, y, op_.p);
 	}
-	static inline void inv(FpT& y, const FpT& x) { op_.fp_invOp(y.v_, x.v_, op_); }
+	static inline void inv(FpT& y, const FpT& x)
+	{
+		assert(!x.isZero());
+		op_.fp_invOp(y.v_, x.v_, op_);
+	}
 	static inline void divBy2(FpT& y, const FpT& x)
 	{
 #if 0
diff --git a/include/mcl/vint.hpp b/include/mcl/vint.hpp
index 1e72600..aed0880 100644
--- a/include/mcl/vint.hpp
+++ b/include/mcl/vint.hpp
@@ -126,6 +126,7 @@ void divNM(T *q, size_t qn, T *r, const T *x, size_t xn, const T *y, size_t yn);
 */
 inline uint32_t divUnit(uint32_t *pr, uint32_t H, uint32_t L, uint32_t y)
 {
+	assert(y != 0);
 	uint64_t t = make64(H, L);
 	uint32_t q = uint32_t(t / y);
 	*pr = uint32_t(t % y);
@@ -134,6 +135,7 @@ inline uint32_t divUnit(uint32_t *pr, uint32_t H, uint32_t L, uint32_t y)
 #if MCL_SIZEOF_UNIT == 8
 inline uint64_t divUnit(uint64_t *pr, uint64_t H, uint64_t L, uint64_t y)
 {
+	assert(y != 0);
 #if defined(MCL_VINT_64BIT_PORTABLE) || (defined(_MSC_VER) && _MSC_VER < 1920)
 	uint32_t px[4] = { uint32_t(L), uint32_t(L >> 32), uint32_t(H), uint32_t(H >> 32) };
 	uint32_t py[2] = { uint32_t(y), uint32_t(y >> 32) };