diff --git a/CHANGELOG.md b/CHANGELOG.md
index 53589708..b5e580b7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -22,6 +22,9 @@ Modifications by (in alphabetical order):
 * P. Vitt, University of Siegen, Germany
 * A. Voysey, UK Met Office
 
+18/08/2026 PR #525 for #524. Fix Io_Implied_Do rejecting a minimal-length
+           io-implied-do such as "(i,i=1,n)" (off-by-one in the length guard).
+
 16/07/2026 PR #520 for #519. Fix truncation of a character length expression that
            contains a comma (e.g. the arguments to an intrinsic such as
            MAX) when the kind appears before the length in a char-selector.
diff --git a/src/fparser/two/Fortran2003.py b/src/fparser/two/Fortran2003.py
index ecc89765..cbf2aa1c 100644
--- a/src/fparser/two/Fortran2003.py
+++ b/src/fparser/two/Fortran2003.py
@@ -9329,7 +9329,9 @@ class Io_Implied_Do(Base):  # R917
 
     @staticmethod
     def match(string):
-        if len(string) <= 9 or string[0] != "(" or string[-1] != ")":
+        # The shortest possible io-implied-do, e.g. "(i,i=1,2)", is 9
+        # characters long.
+        if len(string) < 9 or string[0] != "(" or string[-1] != ")":
             return
         line, repmap = string_replace_map(string[1:-1].strip())
         i = line.rfind("=")
diff --git a/src/fparser/two/tests/test_fortran2003.py b/src/fparser/two/tests/test_fortran2003.py
index cfcefaa1..5ff35a6e 100644
--- a/src/fparser/two/tests/test_fortran2003.py
+++ b/src/fparser/two/tests/test_fortran2003.py
@@ -2228,6 +2228,11 @@ def test_io_implied_do():  # R917
     assert isinstance(obj, tcls), repr(obj)
     assert str(obj) == "(a, i = 1, 2)"
 
+    # Minimal-length (9-character) io-implied-do.
+    obj = tcls("(i,i=1,2)")
+    assert isinstance(obj, tcls), repr(obj)
+    assert str(obj) == "(i, i = 1, 2)"
+
     obj = tcls("((i+j,j=3,4,1), i=1,2)")
     assert isinstance(obj, tcls), repr(obj)
     assert str(obj) == "((i + j, j = 3, 4, 1), i = 1, 2)"