diff --git a/sigv4/README.md b/sigv4/README.md
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+github.com/prometheus/common/sigv4 module
+=========================================
+
+sigv4 provides a http.RoundTripper that will sign requests using
+Amazon's Signature Verification V4 signing procedure, using credentials
+from the default AWS credential chain.
+
+This is a separate module from github.com/prometheus/common to prevent
+it from having and propagating a dependency on the AWS SDK.