diff --git a/simon128_simd.cpp b/simon128_simd.cpp
index a6cdf0d8..29a9b1bc 100644
--- a/simon128_simd.cpp
+++ b/simon128_simd.cpp
@@ -62,6 +62,14 @@ using CryptoPP::vec_swap;  // SunCC
 
 #if (CRYPTOPP_ARM_NEON_AVAILABLE)
 
+// Missing from Microsoft's implementation???
+#if defined(_MSC_VER)
+inline uint64x2_t vld1q_dup_u64(const uint64_t* ptr)
+{
+	return vmovq_n_u64(*ptr);
+}
+#endif
+
 template <class T>
 inline T UnpackHigh64(const T& a, const T& b)
 {
diff --git a/speck128_simd.cpp b/speck128_simd.cpp
index 60ffaf26..2db2a1bb 100644
--- a/speck128_simd.cpp
+++ b/speck128_simd.cpp
@@ -61,6 +61,14 @@ using CryptoPP::word64;
 
 #if (CRYPTOPP_ARM_NEON_AVAILABLE)
 
+// Missing from Microsoft's implementation???
+#if defined(_MSC_VER)
+inline uint64x2_t vld1q_dup_u64(const uint64_t* ptr)
+{
+	return vmovq_n_u64(*ptr);
+}
+#endif
+
 template <class T>
 inline T UnpackHigh64(const T& a, const T& b)
 {