Index: cddl/contrib/opensolaris/lib/libdtrace/common/dt_subr.c
===================================================================
--- cddl/contrib/opensolaris/lib/libdtrace/common/dt_subr.c
+++ cddl/contrib/opensolaris/lib/libdtrace/common/dt_subr.c
@@ -581,6 +581,7 @@
 dt_printf(dtrace_hdl_t *dtp, FILE *fp, const char *format, ...)
 {
 	va_list ap;
+	va_list ap2;
 	int n;
 
 #ifndef illumos
@@ -640,11 +641,14 @@
 			dtp->dt_buffered_buf[0] = '\0';
 		}
 
-		if ((needed = vsnprintf(NULL, 0, format, ap)) < 0) {
+		va_copy(ap2, ap);
+		if ((needed = vsnprintf(NULL, 0, format, ap2)) < 0) {
 			rval = dt_set_errno(dtp, errno);
+			va_end(ap2);
 			va_end(ap);
 			return (rval);
 		}
+		va_end(ap2);
 
 		if (needed == 0) {
 			va_end(ap);
@@ -670,12 +674,15 @@
 			dtp->dt_buffered_size <<= 1;
 		}
 
+		va_copy(ap2, ap);
 		if (vsnprintf(&dtp->dt_buffered_buf[dtp->dt_buffered_offs],
-		    avail, format, ap) < 0) {
+		    avail, format, ap2) < 0) {
 			rval = dt_set_errno(dtp, errno);
+			va_end(ap2);
 			va_end(ap);
 			return (rval);
 		}
+		va_end(ap2);
 
 		dtp->dt_buffered_offs += needed;
 		assert(dtp->dt_buffered_buf[dtp->dt_buffered_offs] == '\0');