diff --git a/src/util/hei_bit_string.cpp b/src/util/hei_bit_string.cpp
index 16713ec..8fc0776 100644
--- a/src/util/hei_bit_string.cpp
+++ b/src/util/hei_bit_string.cpp
@@ -15,9 +15,9 @@
 //##############################################################################
 
 // number of bits in a uint64_t
-constexpr uint64_t BitString::UINT64_BIT_LEN = sizeof(uint64_t) * 8;
+const uint64_t BitString::UINT64_BIT_LEN = sizeof(uint64_t) * 8;
 // number of bits in a uint8_t
-constexpr uint64_t BitString::UINT8_BIT_LEN = sizeof(uint8_t) * 8;
+const uint64_t BitString::UINT8_BIT_LEN = sizeof(uint8_t) * 8;
 
 //------------------------------------------------------------------------------