diff --git a/xs/src/libslic3r/ConditionalGcode.cpp b/xs/src/libslic3r/ConditionalGcode.cpp
index 248f6d359..bfc74a55a 100644
--- a/xs/src/libslic3r/ConditionalGcode.cpp
+++ b/xs/src/libslic3r/ConditionalGcode.cpp
@@ -44,6 +44,7 @@ std::string evaluate(const std::string& expression_string) {
         #if SLIC3R_DEBUG
         std::cerr << __FILE__ << ":" << __LINE__ << " "<< "Failed to parse: " << expression_string.c_str() << std::endl;
         #endif
+        result << "{" << expression_string << "}";
     }
     std::string output = result.str();
     trim(output);
diff --git a/xs/t/24_gcodemath.t b/xs/t/24_gcodemath.t
index 5cee43989..1aeba40d0 100644
--- a/xs/t/24_gcodemath.t
+++ b/xs/t/24_gcodemath.t
@@ -41,6 +41,6 @@ use Test::More tests => 6;
         my $test_string = "M104 S{a}; Sets temp to {4*5}";
 
         my $result = Slic3r::ConditionalGCode::apply_math($test_string);
-        is $result, "M104 S; Sets temp to 20", 'Blank string emittal on failure to parse';
+        is $result, "M104 S{a}; Sets temp to 20", 'Original string emittal on failure to parse';
     }
 }