diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index dbe104df339b..ca9ab8a7a4ee 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -3,18 +3,37 @@
 #define _ASM_X86_CPUFEATURES_H
 
 /*
- * Defines x86 CPU feature bits
+ * Defines x86 CPU feature bits.
+ */
+
+/*
+ * Number of words of features and bugs, respectively.
+ *
+ * These should be even, as these arrays can be accessed by bitmask operations that
+ * use "unsigned long", which is 64 bits on x86-64.
+ *
+ * These must be expressed as decimal constants as they are read
+ * by scripts.
  */
 #define NCAPINTS			22	   /* N 32-bit words worth of info */
 #define NBUGINTS			2	   /* N 32-bit bug flags */
 
+#if (NCAPINTS | NBUGINTS) & 1
+# error "NCAPINTS and NBUGINTS must be even, just increment any odd number by one"
+#endif
+
 /*
- * Note: If the comment begins with a quoted string, that string is used
- * in /proc/cpuinfo instead of the macro name.  Otherwise, this feature
- * bit is not displayed in /proc/cpuinfo at all.
+ * Note: If the comment begins with a quoted string, that string is
+ * displayed in /proc/cpuinfo. Otherwise, this feature bit is not
+ * displayed in /proc/cpuinfo at all.
+ *
+ * This string should be in lower case and match C identifier rules.
  *
  * When adding new features here that depend on other features,
  * please update the table in kernel/cpu/cpuid-deps.c as well.
+ *
+ * As this file is read by scripts, the format of each of these lines
+ * must be strictly followed.
  */
 
 /* Intel-defined CPU features, CPUID level 0x00000001 (EDX), word 0 */