diff --git a/pkg/interp/internal.jq b/pkg/interp/internal.jq
index a929ed41..461e2628 100644
--- a/pkg/interp/internal.jq
+++ b/pkg/interp/internal.jq
@@ -26,7 +26,7 @@ def printerr: tostring | _stderr;
 def printerrln: ., "\n" | printerr;
 
 # jq compat
-def debug: (["DEBUG", .] | tojson | printerrln), .;
+def debug: (["DEBUG:", .] | tojson | printerrln), .;
 def debug(f): (f | debug | empty), .;
 # output raw string or compact json to stderr and let input thru
 def stderr: printerr, .;
diff --git a/pkg/interp/testdata/debug.fqtest b/pkg/interp/testdata/debug.fqtest
index d7e26aed..dcbe9037 100644
--- a/pkg/interp/testdata/debug.fqtest
+++ b/pkg/interp/testdata/debug.fqtest
@@ -11,8 +11,8 @@ null> {a: 123, b: []} | debug({a})
 }
 null> ^D
 stderr:
-["DEBUG",{"a":123,"b":[]}]
-["DEBUG",{"a":123}]
+["DEBUG:",{"a":123,"b":[]}]
+["DEBUG:",{"a":123}]
 $ fq -n 'null, {a:1}, "abc" | ., "\n" | print'
 null
 {"a":1}