--- a/build/moz.configure/toolchain.configure
+++ b/build/moz.configure/toolchain.configure
@@ -76,30 +76,30 @@ add_old_configure_assignment('_YASM_MAJO
 add_old_configure_assignment('_YASM_MINOR_VERSION',
                              yasm_version.minor)
 
 
 @depends(yasm, target)
 def yasm_asflags(yasm, target):
     if yasm:
         asflags = {
-            ('OSX', 'x86'): '-f macho32',
-            ('OSX', 'x86_64'): '-f macho64',
-            ('WINNT', 'x86'): '-f win32',
-            ('WINNT', 'x86_64'): '-f x64',
+            ('OSX', 'x86'): ['-f', 'macho32'],
+            ('OSX', 'x86_64'): ['-f', 'macho64'],
+            ('WINNT', 'x86'): ['-f', 'win32'],
+            ('WINNT', 'x86_64'): ['-f', 'x64'],
         }.get((target.os, target.cpu), None)
         if asflags is None:
             # We're assuming every x86 platform we support that's
             # not Windows or Mac is ELF.
             if target.cpu == 'x86':
-                asflags = '-f elf32'
+                asflags = ['-f', 'elf32']
             elif target.cpu == 'x86_64':
-                asflags = '-f elf64'
+                asflags = ['-f', 'elf64']
         if asflags:
-            asflags += ' -rnasm -pnasm'
+            asflags += ['-rnasm', '-pnasm']
         return asflags
 
 
 set_config('YASM_ASFLAGS', yasm_asflags)
 
 
 @depends(yasm_asflags)
 def have_yasm(value):

--- a/js/src/old-configure.in
+++ b/js/src/old-configure.in
@@ -1947,17 +1947,17 @@ dnl =
 dnl = Maintainer debug option (no --enable equivalent)
 dnl =
 dnl ========================================================
 
 AC_SUBST(AR)
 AC_SUBST(AR_FLAGS)
 AC_SUBST(AR_EXTRACT)
 AC_SUBST(AS)
-AC_SUBST(ASFLAGS)
+AC_SUBST_LIST(ASFLAGS)
 AC_SUBST(AS_DASH_C_FLAG)
 AC_SUBST(RC)
 AC_SUBST(RCFLAGS)
 AC_SUBST(WINDRES)
 AC_SUBST(IMPLIB)
 AC_SUBST(FILTER)
 AC_SUBST_LIST(MOZ_DEBUG_LDFLAGS)
 AC_SUBST(WARNINGS_AS_ERRORS)

--- a/old-configure.in
+++ b/old-configure.in
@@ -4473,17 +4473,17 @@ dnl =
 dnl = Maintainer debug option (no --enable equivalent)
 dnl =
 dnl ========================================================
 
 AC_SUBST(AR)
 AC_SUBST(AR_FLAGS)
 AC_SUBST(AR_EXTRACT)
 AC_SUBST(AS)
-AC_SUBST(ASFLAGS)
+AC_SUBST_LIST(ASFLAGS)
 AC_SUBST(AS_DASH_C_FLAG)
 AC_SUBST(RC)
 AC_SUBST(RCFLAGS)
 AC_SUBST(WINDRES)
 AC_SUBST(IMPLIB)
 AC_SUBST(FILTER)
 AC_SUBST(MOZ_AUTH_EXTENSION)
 AC_SUBST(MOZ_PREF_EXTENSIONS)