diff --git a/packages/myst-parser/tests/roles/si.yml b/packages/myst-parser/tests/roles/si.yml
index 180eeb071..606123195 100644
--- a/packages/myst-parser/tests/roles/si.yml
+++ b/packages/myst-parser/tests/roles/si.yml
@@ -32,3 +32,22 @@ cases:
                   unit: Hz
                   units: [hertz]
                   value: 100 Hz
+
+
+  - title: decimal number parses
+    markdown: '{si}`1.345e10 <\hertz>`'
+    mdast:
+      type: root
+      children:
+        - type: paragraph
+          children:
+            - type: mystRole
+              name: si
+              value: 1.345e10 <\hertz>
+              children:
+                - type: si
+                  alt: hertz
+                  number: '1.345e10'
+                  unit: Hz
+                  units: [hertz]
+                  value: 1.345e10 Hz
\ No newline at end of file
diff --git a/packages/myst-roles/src/si.ts b/packages/myst-roles/src/si.ts
index 44ae6d0bc..f15b35933 100644
--- a/packages/myst-roles/src/si.ts
+++ b/packages/myst-roles/src/si.ts
@@ -9,11 +9,12 @@ export const siRole: RoleSpec = {
   },
   run(data: RoleData): GenericNode[] {
     const value = data.body as string;
-    const match = value.match(/([0-9]+)\s?<([\\a-zA-Z\s]+)>/);
+    const match = value.match(/(-?\d+(,\d+)*(\.\d+(e\d+)?)?)\s?<([\\a-zA-Z\s]+)>/);
     if (!match) {
       return [{ type: 'si', error: true, value }];
     }
-    const [, number, commands] = match;
+    const number = match[1];
+    const commands = match[match.length-1];
     const parsed = [...commands.matchAll(/\\([a-zA-Z]+)/g)];
     const units = parsed.filter((c) => !!c).map(([, c]) => c);
     const translated = units.map((c) => UNITS[c] ?? c);