diff --git a/src/doc/man/rustc.1 b/src/doc/man/rustc.1
index 2a91774d671ac..2731a7257cdd2 100644
--- a/src/doc/man/rustc.1
+++ b/src/doc/man/rustc.1
@@ -62,7 +62,7 @@ Comma separated list of compiler information to print on stdout.
 Equivalent to \fI\-C\ debuginfo=2\fR.
 .TP
 \fB\-O\fR
-Equivalent to \fI\-C\ opt\-level=2\fR.
+Equivalent to \fI\-C\ opt\-level=3\fR.
 .TP
 \fB\-o\fR \fIFILENAME\fR
 Write output to \fIFILENAME\fR. Ignored if multiple \fI\-\-emit\fR outputs are specified which