diff --git a/flang-rt/lib/runtime/namelist.cpp b/flang-rt/lib/runtime/namelist.cpp
index e9c0b8ffa2da2..f30e615e8f0fa 100644
--- a/flang-rt/lib/runtime/namelist.cpp
+++ b/flang-rt/lib/runtime/namelist.cpp
@@ -170,7 +170,9 @@ static RT_API_ATTRS bool HandleSubscripts(IoStatementState &io,
   std::size_t byteCount{0};
   common::optional<char32_t> ch{io.GetNextNonBlank(byteCount)};
   char32_t comma{GetComma(io)};
-  for (; ch && *ch != ')'; ++j) {
+
+  // Read subscripts, but don't exceed rank to prevent buffer overrun.
+  for (int Rank = source.rank(); ch && *ch != ')' && j <= Rank; ++j) {
     SubscriptValue dimLower{0}, dimUpper{0}, dimStride{0};
     if (j < maxRank && j < source.rank()) {
       const Dimension &dim{source.GetDimension(j)};
diff --git a/flang-rt/test/Runtime/bad_subscript_overrun01.f90 b/flang-rt/test/Runtime/bad_subscript_overrun01.f90
new file mode 100644
index 0000000000000..70cc84b168bab
--- /dev/null
+++ b/flang-rt/test/Runtime/bad_subscript_overrun01.f90
@@ -0,0 +1,50 @@
+! Test a buffer overrun when an illegal vector-valued subscript is used in
+! namelist input.
+! The error should be reported through the READ's IOSTAT value.
+! RUN: %flang -L"%libdir" %s -o %t
+! RUN: env LD_LIBRARY_PATH="$LD_LIBRARY_PATH:%libdir" %t | FileCheck %s
+! CHECK-NOT: FAIL
+
+PROGRAM bad_subscript_overrun01
+  IMPLICIT NONE
+
+  INTEGER,DIMENSION(5)                :: U, EXPECTU
+  INTEGER,DIMENSION(5)                :: V, EXPECTV
+  CHARACTER(LEN=20)                   :: NAMELIST_RECORD
+  INTEGER                             :: IOS, ILOOP
+
+  NAMELIST /SCORES/ U
+  NAMELIST /CHTEST/ NAMELIST_RECORD
+
+  U = 8
+  EXPECTU = U
+  V = 9
+  EXPECTV = V
+  IOS = 0
+
+  NAMELIST_RECORD = " &SCORES U(V) = -1 /"
+  OPEN(UNIT=10, ACCESS='SEQUENTIAL', ACTION='READWRITE')
+  WRITE(10,'(A)') NAMELIST_RECORD
+  REWIND 10
+
+  ! This should fail because of the bad index.
+  READ(10, NML = SCORES, IOSTAT=IOS)
+  CLOSE(UNIT=10, STATUS='KEEP')
+
+  ! Make sure the READ status was a failure.
+  IF(IOS.NE.0) THEN
+    PRINT *, "Test 1 - PASS"
+  ELSE
+    print *, "Test 1 - FAIL"
+  ENDIF
+
+  ! Make sure the values of the array haven't changed.
+  DO ILOOP = 1,5
+    IF(U(ILOOP).EQ.EXPECTU(ILOOP)) THEN
+      PRINT *, "Test 2 - PASS"
+    ELSE
+      PRINT *, "Test 2 - FAIL"
+    ENDIF
+  ENDDO
+
+END PROGRAM bad_subscript_overrun01