diff --git a/src/runtime/Config.x86-64-sunos b/src/runtime/Config.x86-64-sunos
index 9a8b621048..091a2f3de6 100644
--- a/src/runtime/Config.x86-64-sunos
+++ b/src/runtime/Config.x86-64-sunos
@@ -1,5 +1,5 @@
 CC=gcc
-CFLAGS += -m64 -g -Wall -std=gnu89 -D__EXTENSIONS__ -DSVR4 -D_REENTRANT -fno-omit-frame-pointer
+CFLAGS += -m64 -g -Wall -std=gnu89 -D__EXTENSIONS__ -DSVR4 -D_REENTRANT -fno-omit-frame-pointer -D_POSIX_PTHREAD_SEMANTICS
 LINKFLAGS = -m64 -g
 ASFLAGS = -m64 -Wall
 GREP = ggrep
diff --git a/src/runtime/Config.x86-sunos b/src/runtime/Config.x86-sunos
index b83c948e22..10635d163d 100644
--- a/src/runtime/Config.x86-sunos
+++ b/src/runtime/Config.x86-sunos
@@ -10,7 +10,8 @@
 # files for more information.
 
 CC=gcc
-CFLAGS += -g -O2 -Wall -D__EXTENSIONS__ -DSVR4 -D_REENTRANT -fno-omit-frame-pointer
+CFLAGS += -g -O2 -Wall -D__EXTENSIONS__ -DSVR4 -D_REENTRANT -fno-omit-frame-pointer -D_POSIX_PTHREAD_SEMANTICS -m32
+LINKFLAGS += -m32
 GREP = ggrep
 
 ASSEM_SRC = x86-assem.S