diff --git a/contexts/si.jsonld b/contexts/si.jsonld
index 57824a9..8cc8c8e 100644
--- a/contexts/si.jsonld
+++ b/contexts/si.jsonld
@@ -80,7 +80,7 @@
         },
         "defining_equation": {
         	"@id": "si:hasDefiningEquation",
-        	"@type": "date"
+        	"@type": "string"
         },
         "defining_constant": {
 			"@id": "si:hasDefiningConstant",