diff --git a/libc/ia16.inc b/libc/ia16.inc
index 1b947afb9..978c1b365 100644
--- a/libc/ia16.inc
+++ b/libc/ia16.inc
@@ -1,7 +1,7 @@
 # Makefile include for ia16-elf-gcc build
 
 INCLUDES=-I$(TOPDIR)/include -I$(TOPDIR)/libc/include -I$(TOPDIR)/elks/include
-DEFINES=-D__LIBC__ -D__ELKS__
+DEFINES=-D__LIBC__
 LIBOBJS=$(OBJS)
 
 INCS=$(INCLUDES)
diff --git a/libc/include/debug/instrument.h b/libc/include/debug/instrument.h
index 3f4851dc1..fb8c8bbf0 100644
--- a/libc/include/debug/instrument.h
+++ b/libc/include/debug/instrument.h
@@ -1,6 +1,6 @@
 /* ELKS stack trace and instrumentation functions library */
 /* Jan 2023 Greg Haerr */
-#ifdef __ELKS__
+#if defined(__ia16__) || defined(__WATCOMC__)
 #include <sys/cdefs.h>
 #else
 #define noinstrument
diff --git a/libc/include/debug/syms.h b/libc/include/debug/syms.h
index c27c7e6f6..6cee55fd8 100644
--- a/libc/include/debug/syms.h
+++ b/libc/include/debug/syms.h
@@ -1,5 +1,5 @@
 /* ELKS symbol table support */
-#ifdef __ELKS__
+#if defined(__ia16__) || defined(__WATCOMC__)
 #include <sys/cdefs.h>
 #else
 #define noinstrument
diff --git a/libc/watcom.inc b/libc/watcom.inc
index 4b46fcfd4..3f33c2036 100644
--- a/libc/watcom.inc
+++ b/libc/watcom.inc
@@ -10,7 +10,7 @@ endif
 
 INCLUDES = -I$(TOPDIR)/libc/include -I$(TOPDIR)/elks/include
 INCLUDES += -I$(WATCOM)/h
-DEFINES = -D__LIBC__ -D__ELKS__
+DEFINES = -D__LIBC__
 LIBOBJS=$(OBJS:.o=.obj)
 
 include $(TOPDIR)/libc/watcom.model