diff --git a/CHANGES b/CHANGES
index 8bef6dd8e..f05b6ce3c 100644
--- a/CHANGES
+++ b/CHANGES
@@ -3,7 +3,7 @@
 * "make spotless" no longer deletes config.h.in.
 * Unterminated string auto termination.
 * %(el)if(n)idn insensitivity to string quotes difference (#809300).
-* _NASM_FORMAT_ now gives output format chosen for compiling.
+* __NASM_FORMAT__ now gives output format chosen for compiling.
   See test/nasmformat.asm for details and output/out*.c for actual values
   for this macro.
   !!NEEDS DOCUMENTING!!
diff --git a/output/outaout.c b/output/outaout.c
index 495e9ac7c..18746e373 100644
--- a/output/outaout.c
+++ b/output/outaout.c
@@ -877,7 +877,7 @@ static void aout_filename (char *inname, char *outname, efunc error)
 
 static const char *aout_stdmac[] = {
     "%define __SECT__ [section .text]",
-    "%define _NASM_FORMAT_ 'aout'",
+    "%define __NASM_FORMAT__ 'aout'",
     "%macro __NASM_CDecl__ 1",
     "%endmacro",
     NULL
diff --git a/output/outas86.c b/output/outas86.c
index b623a15b2..ccf87e7fa 100644
--- a/output/outas86.c
+++ b/output/outas86.c
@@ -555,7 +555,7 @@ static void as86_filename (char *inname, char *outname, efunc error)
 
 static const char *as86_stdmac[] = {
     "%define __SECT__ [section .text]",
-    "%define _NASM_FORMAT_ 'as86'",
+    "%define __NASM_FORMAT__ 'as86'",
     "%macro __NASM_CDecl__ 1",
     "%endmacro",
     NULL
diff --git a/output/outbin.c b/output/outbin.c
index 72821ffde..3f63d4ce3 100644
--- a/output/outbin.c
+++ b/output/outbin.c
@@ -137,7 +137,7 @@ static char *infile, *outfile;
 
 static const char *bin_stdmac[] = {
    "%define __SECT__ [section .text]",
-   "%define _NASM_FORMAT_ 'bin'",
+   "%define __NASM_FORMAT__ 'bin'",
    "%imacro org 1+.nolist",
    "[org %1]",
    "%endmacro",
diff --git a/output/outcoff.c b/output/outcoff.c
index 655e3fc05..bd0202f2a 100644
--- a/output/outcoff.c
+++ b/output/outcoff.c
@@ -820,7 +820,7 @@ static void coff_win32_filename (char *inname, char *outname, efunc error)
 
 static const char *coff_stdmac[] = {
     "%define __SECT__ [section .text]",
-    "%define _NASM_FORMAT_ 'coff'",
+    "%define __NASM_FORMAT__ 'coff'",
     "%macro __NASM_CDecl__ 1",
     "%endmacro",
     "%imacro export 1+.nolist",
diff --git a/output/outelf.c b/output/outelf.c
index 276feac06..bff9405d0 100644
--- a/output/outelf.c
+++ b/output/outelf.c
@@ -1225,7 +1225,7 @@ static void elf_filename (char *inname, char *outname, efunc error)
 
 static const char *elf_stdmac[] = {
     "%define __SECT__ [section .text]",
-    "%define _NASM_FORMAT_ 'elf'",
+    "%define __NASM_FORMAT__ 'elf'",
     "%macro __NASM_CDecl__ 1",
     "%define $_%1 $%1",
     "%endmacro",
diff --git a/output/outobj.c b/output/outobj.c
index 188ff73e6..a3eed140a 100644
--- a/output/outobj.c
+++ b/output/outobj.c
@@ -2285,7 +2285,7 @@ void obj_fwrite(ObjRecord *orp)
 
 static const char *obj_stdmac[] = {
     "%define __SECT__ [section .text]",
-    "%define _NASM_FORMAT_ 'obj'",
+    "%define __NASM_FORMAT__ 'obj'",
     "%imacro group 1+.nolist",
     "[group %1]",
     "%endmacro",
diff --git a/output/outrdf.c b/output/outrdf.c
index 6ae492ea5..32e63bca5 100644
--- a/output/outrdf.c
+++ b/output/outrdf.c
@@ -501,7 +501,7 @@ static void rdf_filename (char *inname, char *outname, efunc error) {
 
 static char *rdf_stdmac[] = {
     "%define __SECT__ [section .text]",
-    "%define _NASM_FORMAT_ 'oldrdf'", /* Its always oldrdf for consistency with rdf version 2 */
+    "%define __NASM_FORMAT__ 'oldrdf'", /* Its always oldrdf for consistency with rdf version 2 */
     "%imacro library 1+.nolist",
     "[library %1]",
     "%endmacro",
diff --git a/output/outrdf2.c b/output/outrdf2.c
index 8fdf6a444..3c69e0a30 100644
--- a/output/outrdf2.c
+++ b/output/outrdf2.c
@@ -753,7 +753,7 @@ static void rdf2_filename (char *inname, char *outname, efunc error) {
 
 static const char *rdf2_stdmac[] = {
     "%define __SECT__ [section .text]",
-    "%define _NASM_FORMAT_ 'rdf'",
+    "%define __NASM_FORMAT__ 'rdf'",
     "%imacro library 1+.nolist",
     "[library %1]",
     "%endmacro",
diff --git a/test/nasmformat.asm b/test/nasmformat.asm
index decf090ee..82d61c152 100644
--- a/test/nasmformat.asm
+++ b/test/nasmformat.asm
@@ -1,9 +1,9 @@
 
-%if _NASM_FORMAT_ == 'bin'
+%if __NASM_FORMAT__ == 'bin'
 
 db 'This is binary format file'
 
-%elif _NASM_FORMAT_ == 'obj'
+%elif __NASM_FORMAT__ == 'obj'
 
 db 'This is object format file'