diff --git a/examples/test_util/EclOutput.cpp b/examples/test_util/EclOutput.cpp
index f56381823..ccd2a2c53 100644
--- a/examples/test_util/EclOutput.cpp
+++ b/examples/test_util/EclOutput.cpp
@@ -271,7 +271,7 @@ std::string EclOutput::make_real_string(float value) const
 
 std::string EclOutput::make_doub_string(double value) const
 {
-    char buffer [20];
+    char buffer [21];
     sprintf (buffer, "%19.13E", value);
 
     if (value == 0.0) {