diff --git a/openVulkanoCpp/Image/ImageLoaderPnm.cpp b/openVulkanoCpp/Image/ImageLoaderPnm.cpp
index be63e47..277e44a 100644
--- a/openVulkanoCpp/Image/ImageLoaderPnm.cpp
+++ b/openVulkanoCpp/Image/ImageLoaderPnm.cpp
@@ -50,7 +50,7 @@ namespace
 		header.magic -= '0';
 		if (header.magic < 1 || header.magic > 6)
 		{
-			throw std::runtime_error("Unsupported magic number: P" + (header.magic + '0'));
+			throw std::runtime_error(std::string("Unsupported format: P") + std::to_string(header.magic));
 		}
 
 		MaybeSkipComments(stream);
@@ -165,7 +165,7 @@ namespace OpenVulkano::Image
 		}
 		else
 		{
-			throw std::runtime_error("Unsupported format: P" + (header.magic + '0'));
+			throw std::runtime_error(std::string("Unsupported format: P") + std::to_string(header.magic));
 		}
 
 		if (header.magic == 1 || header.magic == 2 || header.magic == 4 || header.magic == 5)