diff --git a/sdk/src/metrics/instrument_metadata_validator.cc b/sdk/src/metrics/instrument_metadata_validator.cc
index 59244bfe33..482330a682 100644
--- a/sdk/src/metrics/instrument_metadata_validator.cc
+++ b/sdk/src/metrics/instrument_metadata_validator.cc
@@ -9,6 +9,8 @@
 
 #if OPENTELEMETRY_HAVE_WORKING_REGEX
 #  include <regex>
+#else
+#  include <algorithm>
 #endif
 
 OPENTELEMETRY_BEGIN_NAMESPACE
@@ -16,11 +18,13 @@ namespace sdk
 {
 namespace metrics
 {
+#if OPENTELEMETRY_HAVE_WORKING_REGEX
 // instrument-name = ALPHA 0*254 ("_" / "." / "-" / "/" / ALPHA / DIGIT)
 const std::string kInstrumentNamePattern = "[a-zA-Z][-_./a-zA-Z0-9]{0,254}";
 //
 const std::string kInstrumentUnitPattern = "[\x01-\x7F]{0,63}";
 // instrument-unit = It can have a maximum length of 63 ASCII chars
+#endif
 
 InstrumentMetaDataValidator::InstrumentMetaDataValidator()
 #if OPENTELEMETRY_HAVE_WORKING_REGEX