diff --git a/libcxx/test/std/input.output/string.streams/stringstream.members/gcount.pass.cpp b/libcxx/test/std/input.output/string.streams/stringstream.members/gcount.pass.cpp
--- a/libcxx/test/std/input.output/string.streams/stringstream.members/gcount.pass.cpp
+++ b/libcxx/test/std/input.output/string.streams/stringstream.members/gcount.pass.cpp
@@ -6,12 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-// All 32 bit arches that CI has:
-//
-// UNSUPPORTED: target=powerpc-ibm-aix
-// UNSUPPORTED: target={{.*}}armv7l{{.*}}
-// UNSUPPORTED: target={{.*}}armv8l{{.*}}
-// UNSUPPORTED: target=i686-w64-windows-gnu
+// UNSUPPORTED: 32-bit
 
 // Test that tellp() does not break the stringstream after INT_MAX, due to use
 // of pbump() that accept int.
diff --git a/libcxx/utils/libcxx/test/features.py b/libcxx/utils/libcxx/test/features.py
--- a/libcxx/utils/libcxx/test/features.py
+++ b/libcxx/utils/libcxx/test/features.py
@@ -381,4 +381,8 @@
   # not other forms of aligned allocation.
   Feature(name='availability-aligned_allocation-missing',
     when=lambda cfg: BooleanExpression.evaluate('stdlib=apple-libc++ && target={{.+}}-apple-macosx10.{{(9|10|11|12)(.0)?}}', cfg.available_features)),
+
+  # Tests that require 64-bit
+  # Fallbacks to 0 if __SIZEOF_SIZE_T__ is not defined
+  Feature(name='32-bit', when=lambda cfg: int(compilerMacros(cfg).get('__SIZEOF_SIZE_T__', 0)) == 4),
 ]