diff --git a/racket/src/ChezScheme/c/version.h b/racket/src/ChezScheme/c/version.h
index 8472375a75..ed5bcd933e 100644
--- a/racket/src/ChezScheme/c/version.h
+++ b/racket/src/ChezScheme/c/version.h
@@ -97,9 +97,11 @@
 #   define LITTLE_ENDIAN_IEEE_DOUBLE
 #  endif
 # elif defined(_MSC_VER) || defined(__MINGW32__)
-#   define OS_ANY_WINDOWS
+#  define OS_ANY_WINDOWS
 # elif __APPLE__
-#   define OS_ANY_MACOSX
+#  define OS_ANY_MACOSX
+# elif defined(sun)
+#  define OS_ANY_SOLARIS2
 # endif
 #endif
 
diff --git a/racket/src/cs/c/configure b/racket/src/cs/c/configure
index dce3e74a6c..2bd596b619 100755
--- a/racket/src/cs/c/configure
+++ b/racket/src/cs/c/configure
@@ -4228,6 +4228,8 @@ disable_curses_arg=--disable-curses
 case "$host_os" in
   solaris2*)
     MACH_OS=s2
+    use_flag_pthread="no"
+    use_flag_posix_pthread="yes"
     ;;
   aix*)
     ;;
diff --git a/racket/src/cs/c/configure.ac b/racket/src/cs/c/configure.ac
index ceea532ac1..b9a60a0159 100644
--- a/racket/src/cs/c/configure.ac
+++ b/racket/src/cs/c/configure.ac
@@ -189,6 +189,8 @@ disable_curses_arg=--disable-curses
 case "$host_os" in
   solaris2*)
     MACH_OS=s2
+    use_flag_pthread="no"
+    use_flag_posix_pthread="yes"
     ;;
   aix*)
     ;;