diff --git a/MsCorePkg/Library/MathLib/MathLib.c b/MsCorePkg/Library/MathLib/MathLib.c
index 1dfa4bae50..3fe27b12e8 100644
--- a/MsCorePkg/Library/MathLib/MathLib.c
+++ b/MsCorePkg/Library/MathLib/MathLib.c
@@ -149,7 +149,7 @@ bsr64 (
   )
 {
  #if __GNUC__ > 3 // if we are using GCC take advantage of their builtins
-  return 64 - __builtin_clzl (value);
+  return 64 - __builtin_clzll (value);
 
  #elif _MSC_VER > 1500 // if we are using MS VS compiler 15 or greater
   unsigned long  result;
diff --git a/MsCorePkg/MsCorePkg.ci.yaml b/MsCorePkg/MsCorePkg.ci.yaml
index 9b239804e7..e3c62e0682 100644
--- a/MsCorePkg/MsCorePkg.ci.yaml
+++ b/MsCorePkg/MsCorePkg.ci.yaml
@@ -109,7 +109,8 @@
             "SQRTUNSIGNED",
             "VARPOL",
             "SNP's",
-            "UEFI's"
+            "UEFI's",
+            "clzll"
         ],
         "AdditionalIncludePaths": [] # Additional paths to spell check relative to package root (wildcards supported)
     },