diff --git a/onnxruntime/core/providers/webnn/builders/helper.cc b/onnxruntime/core/providers/webnn/builders/helper.cc
index 31453e005272e..774df067fe347 100644
--- a/onnxruntime/core/providers/webnn/builders/helper.cc
+++ b/onnxruntime/core/providers/webnn/builders/helper.cc
@@ -53,9 +53,12 @@ bool IsInputSupported(const NodeArg& input, const std::string& parent_name, cons
   }
 
   for (const auto& dim : shape_proto->dim()) {
-    // For now we workaround dynamic shape support by assuming 1.
+    // WebNN doesn't support dynamic shape - use sessionOptions.freeDimensionOverrides to fix the shape.
     if (!dim.has_dim_value()) {
-      LOGS(logger, VERBOSE) << "Dynamic shape is not supported for now, assume to be 1, for input:" << input_name;
+      LOGS(logger, VERBOSE) << "Dynamic shape is not supported, "
+                            << "use sessionOptions.FreeDimensionOverrides to set a fixed shape for input: "
+                            << input_name;
+      return false;
     }
   }
 
diff --git a/onnxruntime/core/providers/webnn/builders/model_builder.cc b/onnxruntime/core/providers/webnn/builders/model_builder.cc
index 14ca4f1a1e674..2eae8cebbbd66 100644
--- a/onnxruntime/core/providers/webnn/builders/model_builder.cc
+++ b/onnxruntime/core/providers/webnn/builders/model_builder.cc
@@ -218,12 +218,9 @@ Status ModelBuilder::RegisterModelInputOutput(const NodeArg& node_arg, bool is_i
     } else {
       dims.reserve(shape.size());
       for (const auto& dim : shape) {
-        if (!dim.has_dim_value()) {
-          // FIXME: support dyanmic shape.
-          dims.push_back(1);
-        } else {
-          dims.push_back(SafeInt<int32_t>(dim.dim_value()));
-        }
+        // dim_param free dimensions should have already been excluded by IsInputSupported().
+        assert(dim.has_dim_value());
+        dims.push_back(SafeInt<int32_t>(dim.dim_value()));
       }
     }
   }