diff --git a/addons/cert.py b/addons/cert.py
index e930b51a5..04cc72c6b 100755
--- a/addons/cert.py
+++ b/addons/cert.py
@@ -231,6 +231,17 @@ def msc30(data):
         if simpleMatch(token, "rand ( )") and isStandardFunction(token):
             reportError(token, 'style', 'Do not use the rand() function for generating pseudorandom numbers', 'MSC30-c')
 
+# STR03-C
+# Do not inadvertently truncate a string
+def str03(data):
+    for token in data.tokenlist:
+        if not isFunctionCall(token, 'strncpy'):
+            continue
+        arguments = cppcheckdata.getArguments(token)
+        if len(arguments)!=3:
+            continue
+        if arguments[2].str=='(' and arguments[2].astOperand1.str=='sizeof':
+            reportError(token, 'style', 'Do not inadvertently truncate a string', 'STR03-C')
 
 # STR05-C
 # Use pointers to const when referring to string literals
@@ -283,6 +294,7 @@ for arg in sys.argv[1:]:
         exp42(cfg)
         exp46(cfg)
         int31(cfg, data.platform)
+        str03(cfg)
         str05(cfg)
         str07(cfg)
         msc30(cfg)
diff --git a/addons/test/cert-test.c b/addons/test/cert-test.c
index 73c409ed4..3763b0736 100644
--- a/addons/test/cert-test.c
+++ b/addons/test/cert-test.c
@@ -61,6 +61,15 @@ void msc30()
     int a = rand;
 }
 
+void str03()
+{
+    char *string_data=(char*)malloc(16);
+    char a[16];
+    int d;
+    strncpy(a, string_data, sizeof(a));     //cert-STR03-C
+    strncpy(a, string_data, 5); d=sizeof(int);
+}
+
 void str05()
 {
     char *str1 = "abc";         //cert-STR05-C