diff --git a/sys/cddl/dev/dtrace/amd64/dtrace_isa.c b/sys/cddl/dev/dtrace/amd64/dtrace_isa.c
index 71b448a99c1c..55e51cee14d8 100644
--- a/sys/cddl/dev/dtrace/amd64/dtrace_isa.c
+++ b/sys/cddl/dev/dtrace/amd64/dtrace_isa.c
@@ -501,11 +501,7 @@ dtrace_getreg(struct trapframe *rp, uint_t reg)
 		REG_SS		/* 18 SS */
 	};
 
-#ifdef illumos
-	if (reg <= SS) {
-#else	/* !illumos */
 	if (reg <= GS) {
-#endif
 		if (reg >= sizeof (regmap) / sizeof (int)) {
 			DTRACE_CPUFLAG_SET(CPU_DTRACE_ILLOP);
 			return (0);
@@ -514,11 +510,7 @@ dtrace_getreg(struct trapframe *rp, uint_t reg)
 		reg = regmap[reg];
 	} else {
 		/* This is dependent on reg.d. */
-#ifdef illumos
-		reg -= SS + 1;
-#else	/* !illumos */
 		reg -= GS + 1;
-#endif
 	}
 
 	switch (reg) {
diff --git a/sys/cddl/dev/dtrace/x86/regset.h b/sys/cddl/dev/dtrace/x86/regset.h
index ad12e26a5aec..b480e411e6c2 100644
--- a/sys/cddl/dev/dtrace/x86/regset.h
+++ b/sys/cddl/dev/dtrace/x86/regset.h
@@ -61,35 +61,6 @@ extern "C" {
 
 #define	REG_GSBASE	27
 #define	REG_FSBASE	26
-#ifdef illumos
-#define	REG_DS		25
-#define	REG_ES		24
-
-#define	REG_GS		23
-#define	REG_FS		22
-#define	REG_SS		21
-#define	REG_RSP		20
-#define	REG_RFL		19
-#define	REG_CS		18
-#define	REG_RIP		17
-#define	REG_ERR		16
-#define	REG_TRAPNO	15
-#define	REG_RAX		14
-#define	REG_RCX		13
-#define	REG_RDX		12
-#define	REG_RBX		11
-#define	REG_RBP		10
-#define	REG_RSI		9
-#define	REG_RDI		8
-#define	REG_R8		7
-#define	REG_R9		6
-#define	REG_R10		5
-#define	REG_R11		4
-#define	REG_R12		3
-#define	REG_R13		2
-#define	REG_R14		1
-#define	REG_R15		0
-#else	/* !illumos */
 #define	REG_SS		25
 #define	REG_RSP		24
 #define	REG_RFL		23
@@ -116,33 +87,11 @@ extern "C" {
 #define	REG_R13		2
 #define	REG_R14		1
 #define	REG_R15		0
-#endif	/* illumos */
 
 /*
  * The names and offsets defined here are specified by i386 ABI suppl.
  */
 
-#ifdef illumos
-#define	SS		18	/* only stored on a privilege transition */
-#define	UESP		17	/* only stored on a privilege transition */
-#define	EFL		16
-#define	CS		15
-#define	EIP		14
-#define	ERR		13
-#define	TRAPNO		12
-#define	EAX		11
-#define	ECX		10
-#define	EDX		9
-#define	EBX		8
-#define	ESP		7
-#define	EBP		6
-#define	ESI		5
-#define	EDI		4
-#define	DS		3
-#define	ES		2
-#define	FS		1
-#define	GS		0
-#else	/* !illumos */
 #define	GS		18
 #define	SS		17	/* only stored on a privilege transition */
 #define	UESP		16	/* only stored on a privilege transition */
@@ -162,7 +111,6 @@ extern "C" {
 #define	DS		2
 #define	ES		1
 #define	FS		0
-#endif	/* illumos */
 
 #define REG_PC  EIP
 #define REG_FP  EBP