diff --git a/mlir/include/mlir/Dialect/OpenACC/OpenACCOps.td b/mlir/include/mlir/Dialect/OpenACC/OpenACCOps.td
--- a/mlir/include/mlir/Dialect/OpenACC/OpenACCOps.td
+++ b/mlir/include/mlir/Dialect/OpenACC/OpenACCOps.td
@@ -565,12 +565,14 @@
     mandatory regions.
 
       1. The initializer region specifies how to initialize the local reduction
-         value. The region has an argument that contains the value of the
+         value. The region has a first argument that contains the value of the
          reduction accumulator at the start of the reduction. It is expected to
-         `acc.yield` the new value.
+         `acc.yield` the new value. Extra arguments
+         can be added to deal with dynamic arrays.
       2. The reduction region contains a sequences of operations to combine two
-         values of the reduction type into one. It has two arguments and it is
-         expected to `acc.yield` the combined value.
+         values of the reduction type into one. It has at least two arguments
+         and it is expected to `acc.yield` the combined value. Extra arguments
+         can be added to deal with dynamic arrays.
 
     Example:
 
diff --git a/mlir/lib/Dialect/OpenACC/IR/OpenACC.cpp b/mlir/lib/Dialect/OpenACC/IR/OpenACC.cpp
--- a/mlir/lib/Dialect/OpenACC/IR/OpenACC.cpp
+++ b/mlir/lib/Dialect/OpenACC/IR/OpenACC.cpp
@@ -377,10 +377,10 @@
   if (region.empty())
     return op->emitOpError() << "expects non-empty " << regionName << " region";
   Block &firstBlock = region.front();
-  if (firstBlock.getNumArguments() != 1 ||
+  if (firstBlock.getNumArguments() < 1 ||
       firstBlock.getArgument(0).getType() != type)
     return op->emitOpError() << "expects " << regionName
-                             << " region with one "
+                             << " region first "
                                 "argument of the "
                              << regionType << " type";
 
@@ -453,11 +453,11 @@
     return emitOpError() << "expects non-empty combiner region";
 
   Block &reductionBlock = getCombinerRegion().front();
-  if (reductionBlock.getNumArguments() != 2 ||
+  if (reductionBlock.getNumArguments() < 2 ||
       reductionBlock.getArgument(0).getType() != getType() ||
       reductionBlock.getArgument(1).getType() != getType())
-    return emitOpError() << "expects combiner region with two arguments of "
-                         << "the reduction type";
+    return emitOpError() << "expects combiner region with the first two "
+                         << "arguments of the reduction type";
 
   for (YieldOp yieldOp : getCombinerRegion().getOps<YieldOp>()) {
     if (yieldOp.getOperands().size() != 1 ||