Fix header guards for moved headers.
diff --git a/runtime/cpp/emboss_arithmetic.h b/runtime/cpp/emboss_arithmetic.h
index c84df17..dd570ba 100644
--- a/runtime/cpp/emboss_arithmetic.h
+++ b/runtime/cpp/emboss_arithmetic.h
@@ -14,8 +14,8 @@
 
 // Implementations for the operations and builtin functions in the Emboss
 // expression language.
-#ifndef EMBOSS_PUBLIC_EMBOSS_ARITHMETIC_H_
-#define EMBOSS_PUBLIC_EMBOSS_ARITHMETIC_H_
+#ifndef EMBOSS_RUNTIME_CPP_EMBOSS_ARITHMETIC_H_
+#define EMBOSS_RUNTIME_CPP_EMBOSS_ARITHMETIC_H_
 
 #include <cstdint>
 #include <type_traits>
@@ -322,4 +322,4 @@
 }  // namespace support
 }  // namespace emboss
 
-#endif  // EMBOSS_PUBLIC_EMBOSS_ARITHMETIC_H_
+#endif  // EMBOSS_RUNTIME_CPP_EMBOSS_ARITHMETIC_H_