diff --git a/sys/amd64/include/atomic.h b/sys/amd64/include/atomic.h
--- a/sys/amd64/include/atomic.h
+++ b/sys/amd64/include/atomic.h
@@ -30,10 +30,6 @@
 #ifndef _MACHINE_ATOMIC_H_
 #define	_MACHINE_ATOMIC_H_
 
-#ifndef _SYS_CDEFS_H_
-#error this file needs sys/cdefs.h as a prerequisite
-#endif
-
 /*
  * To express interprocessor (as opposed to processor and device) memory
  * ordering constraints, use the atomic_*() functions with acquire and release
diff --git a/sys/amd64/include/cpufunc.h b/sys/amd64/include/cpufunc.h
--- a/sys/amd64/include/cpufunc.h
+++ b/sys/amd64/include/cpufunc.h
@@ -41,10 +41,6 @@
 #ifndef _MACHINE_CPUFUNC_H_
 #define	_MACHINE_CPUFUNC_H_
 
-#ifndef _SYS_CDEFS_H_
-#error this file needs sys/cdefs.h as a prerequisite
-#endif
-
 struct region_descriptor;
 
 #define readb(va)	(*(volatile uint8_t *) (va))
diff --git a/sys/amd64/include/pcpu.h b/sys/amd64/include/pcpu.h
--- a/sys/amd64/include/pcpu.h
+++ b/sys/amd64/include/pcpu.h
@@ -31,10 +31,6 @@
 #ifndef _MACHINE_PCPU_H_
 #define	_MACHINE_PCPU_H_
 
-#ifndef _SYS_CDEFS_H_
-#error "sys/cdefs.h is a prerequisite for this file"
-#endif
-
 #include <machine/segments.h>
 #include <machine/tss.h>
 
diff --git a/sys/arm/include/armreg.h b/sys/arm/include/armreg.h
--- a/sys/arm/include/armreg.h
+++ b/sys/arm/include/armreg.h
@@ -43,10 +43,6 @@
 #ifndef MACHINE_ARMREG_H
 #define MACHINE_ARMREG_H
 
-#ifndef _SYS_CDEFS_H_
-#error Please include sys/cdefs.h before including machine/armreg.h
-#endif
-
 #define INSN_SIZE	4
 #define INSN_COND_MASK	0xf0000000	/* Condition mask */
 #define PSR_MODE        0x0000001f      /* mode mask */
diff --git a/sys/i386/include/atomic.h b/sys/i386/include/atomic.h
--- a/sys/i386/include/atomic.h
+++ b/sys/i386/include/atomic.h
@@ -30,10 +30,6 @@
 #ifndef _MACHINE_ATOMIC_H_
 #define	_MACHINE_ATOMIC_H_
 
-#ifndef _SYS_CDEFS_H_
-#error this file needs sys/cdefs.h as a prerequisite
-#endif
-
 #include <sys/atomic_common.h>
 
 #ifdef _KERNEL
diff --git a/sys/i386/include/cpufunc.h b/sys/i386/include/cpufunc.h
--- a/sys/i386/include/cpufunc.h
+++ b/sys/i386/include/cpufunc.h
@@ -40,10 +40,6 @@
 #ifndef _MACHINE_CPUFUNC_H_
 #define	_MACHINE_CPUFUNC_H_
 
-#ifndef _SYS_CDEFS_H_
-#error this file needs sys/cdefs.h as a prerequisite
-#endif
-
 struct region_descriptor;
 
 #define readb(va)	(*(volatile uint8_t *) (va))
diff --git a/sys/i386/include/pcpu.h b/sys/i386/include/pcpu.h
--- a/sys/i386/include/pcpu.h
+++ b/sys/i386/include/pcpu.h
@@ -31,10 +31,6 @@
 #ifndef _MACHINE_PCPU_H_
 #define	_MACHINE_PCPU_H_
 
-#ifndef _SYS_CDEFS_H_
-#error "sys/cdefs.h is a prerequisite for this file"
-#endif
-
 #include <machine/segments.h>
 #include <machine/tss.h>
 
diff --git a/sys/powerpc/include/atomic.h b/sys/powerpc/include/atomic.h
--- a/sys/powerpc/include/atomic.h
+++ b/sys/powerpc/include/atomic.h
@@ -34,10 +34,6 @@
 #ifndef _MACHINE_ATOMIC_H_
 #define	_MACHINE_ATOMIC_H_
 
-#ifndef _SYS_CDEFS_H_
-#error this file needs sys/cdefs.h as a prerequisite
-#endif
-
 #include <sys/atomic_common.h>
 
 #ifndef __powerpc64__
diff --git a/sys/riscv/include/profile.h b/sys/riscv/include/profile.h
--- a/sys/riscv/include/profile.h
+++ b/sys/riscv/include/profile.h
@@ -34,10 +34,6 @@
 #ifndef _MACHINE_PROFILE_H_
 #define	_MACHINE_PROFILE_H_
 
-#if !defined(_KERNEL) && !defined(_SYS_CDEFS_H_)
-#error this file needs sys/cdefs.h as a prerequisite
-#endif
-
 #define	FUNCTION_ALIGNMENT	32
 
 typedef u_long	fptrdiff_t;
diff --git a/sys/sys/linker_set.h b/sys/sys/linker_set.h
--- a/sys/sys/linker_set.h
+++ b/sys/sys/linker_set.h
@@ -32,10 +32,6 @@
 #ifndef _SYS_LINKER_SET_H_
 #define _SYS_LINKER_SET_H_
 
-#ifndef _SYS_CDEFS_H_
-#error this file needs sys/cdefs.h as a prerequisite
-#endif
-
 /*
  * The following macros are used to declare global sets of objects, which
  * are collected by the linker into a `linker_set' as defined below.
diff --git a/sys/x86/include/x86_ieeefp.h b/sys/x86/include/x86_ieeefp.h
--- a/sys/x86/include/x86_ieeefp.h
+++ b/sys/x86/include/x86_ieeefp.h
@@ -47,10 +47,6 @@
  * XXX: {FP,SSE}*FLD and {FP,SSE}*OFF are undocumented pollution.
  */
 
-#ifndef _SYS_CDEFS_H_
-#error this file needs sys/cdefs.h as a prerequisite
-#endif
-
 /*
  * Rounding modes.
  */