diff --git a/build/autoconf/config.sub b/build/autoconf/config.sub
index 3d9a8dc..2d958b2 100755
--- a/build/autoconf/config.sub
+++ b/build/autoconf/config.sub
@@ -1728,6 +1728,8 @@ case $os in
 	sco3.2v2 | sco3.2v[4-9]* | sco5v6*)
 		# Don't forget version if it is 3.2v4 or newer.
 		;;
+        illumos)
+                ;;
 	none)
 		;;
 	*)
diff --git a/build/moz.configure/init.configure b/build/moz.configure/init.configure
index 3a164c6..f287f5c 100644
--- a/build/moz.configure/init.configure
+++ b/build/moz.configure/init.configure
@@ -716,6 +716,8 @@ def split_triplet(triplet, allow_msvc=False, allow_wasi=False):
         canonical_os = canonical_kernel = "OpenBSD"
     elif os.startswith("solaris"):
         canonical_os = canonical_kernel = "SunOS"
+    elif os.startswith("illumos"):
+        canonical_os = canonical_kernel = "SunOS"
     elif os.startswith("wasi") and allow_wasi:
         canonical_os = canonical_kernel = "WASI"
     else:
@@ -1111,7 +1116,7 @@ def target_is_solaris(target):
         return True
 
 
-set_define("XP_SOLARIS", target_is_solaris)
+set_define("SOLARIS", target_is_solaris)
 
 
 @depends(target)
diff --git a/python/mozbuild/mozbuild/configure/constants.py b/python/mozbuild/mozbuild/configure/constants.py
index 9f7a977..610121f 100644
--- a/python/mozbuild/mozbuild/configure/constants.py
+++ b/python/mozbuild/mozbuild/configure/constants.py
@@ -24,6 +24,7 @@ OS = EnumString.subclass(
         "OpenBSD",
         "OSX",
         "SunOS",
+        "Illumos",
         "WINNT",
         "WASI",
 )
@@ -37,6 +38,7 @@ Kernel = EnumString.subclass(
         "NetBSD",
         "OpenBSD",
         "SunOS",
+        "Illumos",
         "WINNT",
         "WASI",
 )
@@ -113,6 +113,7 @@ kernel_preprocessor_checks = {
     "NetBSD": "__NetBSD__",
     "OpenBSD": "__OpenBSD__",
     "SunOS": "__sun__",
+    "Illumos": "__sun__",
     "WINNT": "_WIN32 || __CYGWIN__",
     "WASI": "__wasi__",
 }