diff --git a/README.md b/README.md
index ff2035f..3900d96 100644
--- a/README.md
+++ b/README.md
@@ -124,7 +124,7 @@ In addition to the common assets server, multiple custom static servers are supp
 2. file provider - setting optional field `assets: true`
 3. docker provider - `reproxy.assets=web-root:location`, i.e. `reproxy.assets=/web:/var/www`.
 
-Assets server supports caching control with the `--assets.cache=<duration>` parameter. `0s` duration (default) turns caching control off. A duration is a sequence of decimal numbers, each with optional fraction and a unit suffix, such as "300ms", "-1.5h" or "2h45m". Valid time units are "ns", "us" (or "µs"), "ms", "s", "m", "h".
+Assets server supports caching control with the `--assets.cache=<duration>` parameter. `0s` duration (default) turns caching control off. A duration is a sequence of decimal numbers, each with optional fraction and a unit suffix, such as "300ms", "1.5h" or "2h45m". Valid time units are "ns", "us" (or "µs"), "ms", "s", "m", "h".
 
 ## More options