diff --git a/libcxx/test/std/diagnostics/syserr/syserr.errcat/syserr.errcat.objects/generic_category.pass.cpp b/libcxx/test/std/diagnostics/syserr/syserr.errcat/syserr.errcat.objects/generic_category.pass.cpp
--- a/libcxx/test/std/diagnostics/syserr/syserr.errcat/syserr.errcat.objects/generic_category.pass.cpp
+++ b/libcxx/test/std/diagnostics/syserr/syserr.errcat/syserr.errcat.objects/generic_category.pass.cpp
@@ -8,7 +8,6 @@
 
 // XFAIL: suse-linux-enterprise-server-11
 // XFAIL: use_system_cxx_lib && target={{.+}}-apple-macosx10.{{9|10|11|12}}
-// XFAIL: LIBCXX-AIX-FIXME
 
 // <system_error>
 
@@ -28,7 +27,11 @@
     const std::error_category& e_cat1 = std::generic_category();
     const std::string msg = e_cat1.message(-1);
     // Exact message format varies by platform.
+    #if defined(_AIX)
+    LIBCPP_ASSERT(msg.rfind("Error -1 occurred", 0) == 0);
+    #else
     LIBCPP_ASSERT(msg.rfind("Unknown error", 0) == 0);
+    #endif
     assert(errno == E2BIG);
 }
 
diff --git a/libcxx/test/std/diagnostics/syserr/syserr.errcat/syserr.errcat.objects/system_category.pass.cpp b/libcxx/test/std/diagnostics/syserr/syserr.errcat/syserr.errcat.objects/system_category.pass.cpp
--- a/libcxx/test/std/diagnostics/syserr/syserr.errcat/syserr.errcat.objects/system_category.pass.cpp
+++ b/libcxx/test/std/diagnostics/syserr/syserr.errcat/syserr.errcat.objects/system_category.pass.cpp
@@ -14,7 +14,6 @@
 
 // XFAIL: suse-linux-enterprise-server-11
 // XFAIL: use_system_cxx_lib && target={{.+}}-apple-macosx10.{{9|10|11|12}}
-// XFAIL: LIBCXX-AIX-FIXME
 
 #include <system_error>
 #include <cassert>
@@ -28,7 +27,11 @@
     const std::error_category& e_cat1 = std::system_category();
     const std::string msg = e_cat1.message(-1);
     // Exact message format varies by platform.
+    #if defined(_AIX)
+    LIBCPP_ASSERT(msg.rfind("Error -1 occurred", 0) == 0);
+    #else
     LIBCPP_ASSERT(msg.rfind("Unknown error", 0) == 0);
+    #endif
     assert(errno == E2BIG);
 }