diff --git a/mlir/include/mlir-c/IR.h b/mlir/include/mlir-c/IR.h
--- a/mlir/include/mlir-c/IR.h
+++ b/mlir/include/mlir-c/IR.h
@@ -505,6 +505,11 @@
 /// Returns the number of arguments of the block.
 MLIR_CAPI_EXPORTED intptr_t mlirBlockGetNumArguments(MlirBlock block);
 
+/// Appends an argument of the specified type to the block. Returns the newly
+/// added argument.
+MLIR_CAPI_EXPORTED MlirValue mlirBlockAddArgument(MlirBlock block,
+                                                  MlirType type);
+
 /// Returns `pos`-th argument of the block.
 MLIR_CAPI_EXPORTED MlirValue mlirBlockGetArgument(MlirBlock block,
                                                   intptr_t pos);
diff --git a/mlir/lib/CAPI/IR/IR.cpp b/mlir/lib/CAPI/IR/IR.cpp
--- a/mlir/lib/CAPI/IR/IR.cpp
+++ b/mlir/lib/CAPI/IR/IR.cpp
@@ -525,6 +525,10 @@
   return static_cast<intptr_t>(unwrap(block)->getNumArguments());
 }
 
+MlirValue mlirBlockAddArgument(MlirBlock block, MlirType type) {
+  return wrap(unwrap(block)->addArgument(unwrap(type)));
+}
+
 MlirValue mlirBlockGetArgument(MlirBlock block, intptr_t pos) {
   return wrap(unwrap(block)->getArgument(static_cast<unsigned>(pos)));
 }
diff --git a/mlir/test/CAPI/ir.c b/mlir/test/CAPI/ir.c
--- a/mlir/test/CAPI/ir.c
+++ b/mlir/test/CAPI/ir.c
@@ -128,7 +128,8 @@
   mlirBlockAppendOwnedOperation(funcBody, dim);
 
   MlirRegion loopBodyRegion = mlirRegionCreate();
-  MlirBlock loopBody = mlirBlockCreate(/*nArgs=*/1, &indexType);
+  MlirBlock loopBody = mlirBlockCreate(0, NULL);
+  mlirBlockAddArgument(loopBody, indexType);
   mlirRegionAppendOwnedBlock(loopBodyRegion, loopBody);
 
   MlirAttribute indexOneLiteral =