diff --git a/cmake/config.h.in b/cmake/config.h.in
index 9c250b4c..203f0afd 100644
--- a/cmake/config.h.in
+++ b/cmake/config.h.in
@@ -21,6 +21,9 @@
 /* Define if building "fat" runtime. */
 #cmakedefine FAT_RUNTIME
 
+/* Define if building AVX-512 in the fat runtime. */
+#cmakedefine BUILD_AVX512
+
 /* Define to 1 if `backtrace' works. */
 #cmakedefine HAVE_BACKTRACE
 
diff --git a/src/util/cpuid_flags.c b/src/util/cpuid_flags.c
index c0ab09af..3c62c07b 100644
--- a/src/util/cpuid_flags.c
+++ b/src/util/cpuid_flags.c
@@ -192,7 +192,8 @@ u64a cpuid_flags(void) {
     cap &= ~HS_CPU_FEATURES_AVX2;
 #endif
 
-#if !defined(FAT_RUNTIME) && !defined(HAVE_AVX512)
+#if (!defined(FAT_RUNTIME) && !defined(HAVE_AVX512)) ||                        \
+    (defined(FAT_RUNTIME) && !defined(BUILD_AVX512))
     cap &= ~HS_CPU_FEATURES_AVX512;
 #endif