diff --git a/Make.sysdefs b/Make.sysdefs
index 05c2c6a6..5499b587 100644
--- a/Make.sysdefs
+++ b/Make.sysdefs
@@ -79,7 +79,7 @@ HPUXLFLAGS =
 HPUXMASTER = GLOBALCFLAGS="$(HPUXCFLAGS)" GLOBALLFLAGS="$(HPUXLFLAGS)" RANLIB="$(HPUXRANLIB)" CLIENTLIBS=-ltermcap
 
 IRIX5RANLIB = echo
-IRIX5CFLAGS = -DSVR4 -DRel4 -DUCONTEXT -O3 -fullwarn -woff 835,709
+IRIX5CFLAGS = -DSVR4 -DRel4 -DUCONTEXT -DMAKECONTEXT_SP_HIGH -O3 -fullwarn -woff 835,709
 IRIX5LFLAGS = -lnsl
 IRIX5MASTER = GLOBALCFLAGS="$(IRIX5CFLAGS)" GLOBALLFLAGS="$(IRIX5LFLAGS)" RANLIB="$(IRIX5RANLIB)"
 
@@ -96,7 +96,8 @@ RTPCCFLAGS = -DBSD_INCLUDES -Daix -Dsys5 $(LOCALCFLAGS) -a
 RTPCLFLAGS = 
 RTPCMASTER = GLOBALCFLAGS="$(RTPCCFLAGS)" GLOBALLFLAGS="$(RTPCLFLAGS)"
 
-SOLCFLAGS = -g -DSVR4 -DRel4 -DUCONTEXT -Dsolaris
+# FIXME -DMAKECONTEXT_SP_HIGH is wrong for Solaris 10.
+SOLCFLAGS = -g -DSVR4 -DRel4 -DUCONTEXT -DMAKECONTEXT_SP_HIGH -Dsolaris
 SOLLFLAGS = -lnsl -lsocket -lthread
 SOLMASTER = GLOBALCFLAGS="$(SOLCFLAGS)" GLOBALLFLAGS="$(SOLLFLAGS)"
 
diff --git a/src/lib/lwp/arch.c b/src/lib/lwp/arch.c
index 222e7d34..9c70d5ea 100644
--- a/src/lib/lwp/arch.c
+++ b/src/lib/lwp/arch.c
@@ -79,6 +79,13 @@ lwpNewContext(struct lwpProc *newp, int stacksz)
     }
     newp->context.uc_stack.ss_sp = newp->ustack;
     newp->context.uc_stack.ss_size = newp->usize;
+#ifdef MAKECONTEXT_SP_HIGH
+    /*
+     * Known systems that are broken that way: Solaris prior to 10,
+     * IRIX.
+     */
+    newp->context.uc_stack.ss_sp += stacksz - 8;
+#endif
     newp->context.uc_stack.ss_flags = 0;
     newp->context.uc_link = NULL;
     makecontext(&newp->context, lwpEntryPoint, 0);