diff --git a/src/backend/utils/misc/guc-file.l b/src/backend/utils/misc/guc-file.l
index 41d62a9f23..6727f1952f 100644
--- a/src/backend/utils/misc/guc-file.l
+++ b/src/backend/utils/misc/guc-file.l
@@ -76,7 +76,7 @@ UNIT_LETTER		[a-zA-Z]
 INTEGER			{SIGN}?({DIGIT}+|0x{HEXDIGIT}+){UNIT_LETTER}*
 
 EXPONENT		[Ee]{SIGN}?{DIGIT}+
-REAL			{SIGN}?{DIGIT}*"."{DIGIT}*{EXPONENT}?
+REAL			{SIGN}?{DIGIT}*("."{DIGIT}*{EXPONENT}?|{EXPONENT}){UNIT_LETTER}*
 
 LETTER			[A-Za-z_\200-\377]
 LETTER_OR_DIGIT [A-Za-z_0-9\200-\377]