diff --git a/prism/src/hybrid/PrismHybrid.cc b/prism/src/hybrid/PrismHybrid.cc
index fe340ff7..f2535829 100644
--- a/prism/src/hybrid/PrismHybrid.cc
+++ b/prism/src/hybrid/PrismHybrid.cc
@@ -58,7 +58,7 @@ static jmethodID main_log_warn = NULL;
 static jmethodID tech_log_mid = NULL;
 
 // error message
-char error_message[MAX_ERR_STRING_LEN];
+static char error_message[MAX_ERR_STRING_LEN];
 
 // details from numerical computation which may be queried
 double last_unif;
diff --git a/prism/src/mtbdd/PrismMTBDD.cc b/prism/src/mtbdd/PrismMTBDD.cc
index bded3276..c9de1aa3 100644
--- a/prism/src/mtbdd/PrismMTBDD.cc
+++ b/prism/src/mtbdd/PrismMTBDD.cc
@@ -63,7 +63,7 @@ FILE *export_file;
 JNIEnv *export_env;
 
 // error message
-char error_message[MAX_ERR_STRING_LEN];
+static char error_message[MAX_ERR_STRING_LEN];
 
 //------------------------------------------------------------------------------
 // cudd manager
diff --git a/prism/src/sparse/PrismSparse.cc b/prism/src/sparse/PrismSparse.cc
index b512bbb0..3d11d2dc 100644
--- a/prism/src/sparse/PrismSparse.cc
+++ b/prism/src/sparse/PrismSparse.cc
@@ -64,7 +64,7 @@ FILE *export_file;
 JNIEnv *export_env;
 
 // error message
-char error_message[MAX_ERR_STRING_LEN];
+static char error_message[MAX_ERR_STRING_LEN];
 
 //------------------------------------------------------------------------------
 // cudd manager