diff --git a/flang/docs/Extensions.md b/flang/docs/Extensions.md
index 4953186c71127..4a038742ddb3f 100644
--- a/flang/docs/Extensions.md
+++ b/flang/docs/Extensions.md
@@ -217,6 +217,8 @@ end
 * At runtime, `NAMELIST` input will skip over `NAMELIST` groups
   with other names, and will treat text before and between groups
   as if they were comment lines, even if not begun with `!`.
+* Commas are required in FORMAT statements and character variables
+  only when they prevent ambiguity.
 
 ### Extensions supported when enabled by options
 
diff --git a/flang/runtime/format-implementation.h b/flang/runtime/format-implementation.h
index 6b1a64b96a851..11f3ad7d18e44 100644
--- a/flang/runtime/format-implementation.h
+++ b/flang/runtime/format-implementation.h
@@ -301,8 +301,14 @@ int FormatControl<CONTEXT>::CueUpNextDataEdit(Context &context, bool stop) {
       if (ch != 'P') { // 1PE5.2 - comma not required (C1302)
         CharType peek{Capitalize(PeekNext())};
         if (peek >= 'A' && peek <= 'Z') {
-          next = peek;
-          ++offset_;
+          if (ch == 'A' /* anticipate F'202X AT editing */ || ch == 'B' ||
+              ch == 'D' || ch == 'E' || ch == 'R' || ch == 'S' || ch == 'T') {
+            // Assume a two-letter edit descriptor
+            next = peek;
+            ++offset_;
+          } else {
+            // extension: assume a comma between 'ch' and 'peek'
+          }
         }
       }
       if ((!next &&