diff --git a/docs/spec/api.md b/docs/spec/api.md
index 605af5a4..747b4f81 100644
--- a/docs/spec/api.md
+++ b/docs/spec/api.md
@@ -334,7 +334,7 @@ digest. The _hex_ portion is the hex-encoded result of the hash.
 We define a _digest_ string to match the following grammar:
 ```
 digest      := algorithm ":" hex
-algorithm   := /[A-Fa-f0-9_+.-]+/
+algorithm   := /[A-Za-z0-9_+.-]+/
 hex         := /[A-Fa-f0-9]+/
 ```
 
diff --git a/docs/spec/api.md.tmpl b/docs/spec/api.md.tmpl
index 9dce5f5b..7fcc566e 100644
--- a/docs/spec/api.md.tmpl
+++ b/docs/spec/api.md.tmpl
@@ -334,7 +334,7 @@ digest. The _hex_ portion is the hex-encoded result of the hash.
 We define a _digest_ string to match the following grammar:
 ```
 digest      := algorithm ":" hex
-algorithm   := /[A-Fa-f0-9_+.-]+/
+algorithm   := /[A-Za-z0-9_+.-]+/
 hex         := /[A-Fa-f0-9]+/
 ```