diff --git a/disas/libvixl/vixl/a64/disasm-a64.cc b/disas/libvixl/vixl/a64/disasm-a64.cc
index 7a58a5c087..f34d1d68da 100644
--- a/disas/libvixl/vixl/a64/disasm-a64.cc
+++ b/disas/libvixl/vixl/a64/disasm-a64.cc
@@ -2985,6 +2985,10 @@ int Disassembler::SubstituteImmediateField(const Instruction* instr,
           }
           return 3;
         }
+        default: {
+          VIXL_UNIMPLEMENTED();
+          return 0;
+        }
       }
     }
     case 'C': {  // ICondB - Immediate Conditional Branch.
diff --git a/disas/libvixl/vixl/globals.h b/disas/libvixl/vixl/globals.h
index 61dc9f7f7e..7099aa599f 100644
--- a/disas/libvixl/vixl/globals.h
+++ b/disas/libvixl/vixl/globals.h
@@ -108,10 +108,12 @@ inline void USE(T1, T2, T3, T4) {}
   #define __has_warning(x)  0
 #endif
 
-// Note: This option is only available for Clang. And will only be enabled for
-// C++11(201103L).
+// Fallthrough annotation for Clang and C++11(201103L).
 #if __has_warning("-Wimplicit-fallthrough") && __cplusplus >= 201103L
   #define VIXL_FALLTHROUGH() [[clang::fallthrough]] //NOLINT
+// Fallthrough annotation for GCC >= 7.
+#elif __GNUC__ >= 7
+  #define VIXL_FALLTHROUGH() __attribute__((fallthrough))
 #else
   #define VIXL_FALLTHROUGH() do {} while (0)
 #endif