diff --git a/apps/restconf/restconf_methods_post.c b/apps/restconf/restconf_methods_post.c
index 735dd6e7..0b06e295 100644
--- a/apps/restconf/restconf_methods_post.c
+++ b/apps/restconf/restconf_methods_post.c
@@ -324,7 +324,10 @@ api_data_post(clicon_handle h,
 	goto done;
     /* ybot is parent of spec(parent(data))) */
     if (ymoddata && (ydata = xml_spec(xdata)) != NULL){
-	if (ys_real_module(ydata) != ymoddata){
+	yang_stmt *ymod = NULL;
+	if (ys_real_module(ydata, &ymod) < 0)
+	    goto done;
+	if (ymod != ymoddata){
 	     if (netconf_malformed_message_xml(&xerr, "Data is not prefixed with matching namespace") < 0)
 		 goto done;
 	     if ((xe = xpath_first(xerr, NULL, "rpc-error")) == NULL){
diff --git a/lib/clixon/clixon_yang.h b/lib/clixon/clixon_yang.h
index bc7fc3e2..48ef85b7 100644
--- a/lib/clixon/clixon_yang.h
+++ b/lib/clixon/clixon_yang.h
@@ -215,7 +215,7 @@ yang_stmt *yn_each(yang_stmt *yn, yang_stmt *ys);
 char      *yang_key2str(int keyword);
 int        ys_module_by_xml(yang_stmt *ysp, struct xml *xt, yang_stmt **ymodp);
 yang_stmt *ys_module(yang_stmt *ys);
-yang_stmt *ys_real_module(yang_stmt *ys);
+int        ys_real_module(yang_stmt *ys, yang_stmt **ymod);
 yang_stmt *ys_spec(yang_stmt *ys);
 yang_stmt *yang_find(yang_stmt *yn, int keyword, const char *argument);
 int        yang_match(yang_stmt *yn, int keyword, char *argument);
diff --git a/lib/src/clixon_json.c b/lib/src/clixon_json.c
index ab1abba5..2b40ca69 100644
--- a/lib/src/clixon_json.c
+++ b/lib/src/clixon_json.c
@@ -716,12 +716,13 @@ xml2json1_cbuf(cbuf                   *cb,
     enum childtype   childt;
     enum array_element_type xc_arraytype;
     yang_stmt       *ys;
-    yang_stmt       *ymod; /* yang module */
+    yang_stmt       *ymod = NULL; /* yang module */
     int              commas;
     char            *modname = NULL;
 
     if ((ys = xml_spec(x)) != NULL){
-	ymod = ys_real_module(ys);
+	if (ys_real_module(ys, &ymod) < 0)
+	    goto done;
 	modname = yang_argument_get(ymod);
 	if (modname0 && strcmp(modname, modname0) == 0)
 	    modname=NULL;
diff --git a/lib/src/clixon_path.c b/lib/src/clixon_path.c
index 672230f1..04d9d3e2 100644
--- a/lib/src/clixon_path.c
+++ b/lib/src/clixon_path.c
@@ -298,11 +298,12 @@ yang2api_path_fmt_1(yang_stmt *ys,
 		    cbuf      *cb)
 {
     yang_stmt *yp; /* parent */
-    yang_stmt *ymod;
+    yang_stmt *ymod = NULL;
+    yang_stmt *ypmod = NULL;
     int        i;
     cvec      *cvk = NULL; /* vector of index keys */
     int        retval = -1;
-
+    
     if ((yp = yang_parent_get(ys)) == NULL){
 	clicon_err(OE_YANG, EINVAL, "yang expected parent %s", yang_argument_get(ys));
 	goto done;
@@ -329,7 +330,11 @@ yang2api_path_fmt_1(yang_stmt *ys,
 		cprintf(cb, "/");
 	}
 	/* If parent namespace/module is different from child -> add child prefix */
-	if (ys_real_module(yp) != (ymod = ys_real_module(ys)))
+	if (ys_real_module(yp, &ypmod) < 0)
+	    goto done;
+	if (ys_real_module(ys, &ymod) < 0)
+	    goto done;
+	if (ypmod != ymod)
 	    cprintf(cb, "%s:", yang_argument_get(ymod));
     }
     else /* top symbol - mark with name prefix */
diff --git a/lib/src/clixon_yang.c b/lib/src/clixon_yang.c
index 15ab9767..be5585d3 100644
--- a/lib/src/clixon_yang.c
+++ b/lib/src/clixon_yang.c
@@ -882,9 +882,10 @@ yang_find_schemanode(yang_stmt *yn,
 }
 
 /*! Given a yang statement, find the prefix associated to this module
+ *
  * @param[in]  ys        Yang statement in module tree (or module itself)
- * @retval     NULL      Not found
- * @retval     prefix    Prefix as char* pointer into yang tree
+ * @retval     NULL      No prefix found. This is an error
+ * @retval     prefix    OK: Prefix as char* pointer into yang tree
  * @code
  * char *myprefix;
  * myprefix = yang_find_myprefix(ys);
@@ -893,25 +894,26 @@ yang_find_schemanode(yang_stmt *yn,
 char *
 yang_find_myprefix(yang_stmt *ys)
 {
-    yang_stmt *ymod; /* My module */
+    yang_stmt *ymod = NULL; /* My module */
     yang_stmt *yprefix;
     char      *prefix = NULL;
 
     /* Not good enough with submodule, must be actual module */
-    if ((ymod = ys_real_module(ys)) == NULL){
-	clicon_err(OE_YANG, 0, "My yang module not found");
+    if (ys_real_module(ys, &ymod) < 0)
+	goto done;
+    if ((yprefix = yang_find(ymod, Y_PREFIX, NULL)) == NULL){
+	clicon_err(OE_YANG, ENOENT, "No prefix found for module %s", yang_argument_get(ymod));
 	goto done;
     }
-    if ((yprefix = yang_find(ymod, Y_PREFIX, NULL)) == NULL)
-	goto done;
     prefix = yang_argument_get(yprefix);
  done:
     return prefix;
 }
 
 /*! Given a yang statement, find the namespace URI associated to this module
+ *
  * @param[in]  ys        Yang statement in module tree (or module itself)
- * @retval     NULL      Not found
+ * @retval     NULL      Error: No namespace found. This is an error
  * @retval     ns        Namspace URI as char* pointer into yang tree
  * @code
  * char *myns = yang_find_mynamespace(ys);
@@ -921,16 +923,16 @@ yang_find_myprefix(yang_stmt *ys)
 char *
 yang_find_mynamespace(yang_stmt *ys)
 {
-    yang_stmt *ymod; /* My module */
+    yang_stmt *ymod = NULL; /* My module */
     yang_stmt *ynamespace;
     char      *ns = NULL;
 
-    if ((ymod = ys_real_module(ys)) == NULL){
-	clicon_err(OE_YANG, ENOENT, "My yang module not found");
+    if (ys_real_module(ys, &ymod) < 0)
+	goto done;
+    if ((ynamespace = yang_find(ymod, Y_NAMESPACE, NULL)) == NULL){
+	clicon_err(OE_YANG, ENOENT, "No namespace found for module %s", yang_argument_get(ymod));
 	goto done;
     }
-    if ((ynamespace = yang_find(ymod, Y_NAMESPACE, NULL)) == NULL)
-	goto done;
     ns = yang_argument_get(ynamespace);
  done:
     return ns;
@@ -1254,22 +1256,30 @@ ys_module(yang_stmt *ys)
 /*! Find real top module given a statement in a yang tree
  * With "real" top module means that if sub-module is the top-node,
  * the module that the sub-module belongs-to is found recursively
- * @param[in] ys    Any yang statement in a yang tree
- * @retval    ymod  The top module or sub-module 
+ * @param[in]  ys    Any yang statement in a yang tree
+ * @param[out] ymod  The top module or sub-module 
+ * @retval     0     OK, returned module in ymod
+ * @retval    -1     YANG validation error: all yang statements should have a "real" module
  * @see ys_module
  * @note For an augmented node, the original module is returned
  */
-yang_stmt *
-ys_real_module(yang_stmt *ys)
+int
+ys_real_module(yang_stmt  *ys,
+	       yang_stmt **ymod)
 {
+    int        retval = -1;
     yang_stmt *ym = NULL;
     yang_stmt *yb;
     char      *name;
     yang_stmt *yspec;
 
+    if (ymod == NULL){
+	clicon_err(OE_YANG, EINVAL, "ymod is NULL");
+	goto done;
+    }
     if ((ym = ys_module(ys)) != NULL){
 	yspec = ys_spec(ym);
-	while (yang_keyword_get(ym) == Y_SUBMODULE){
+	while (ym && yang_keyword_get(ym) == Y_SUBMODULE){
 	    if ((yb = yang_find(ym, Y_BELONGS_TO, NULL)) == NULL){
 		clicon_err(OE_YANG, ENOENT, "No belongs-to statement of submodule %s", yang_argument_get(ym)); /* shouldnt happen */
 		goto done;
@@ -1278,12 +1288,14 @@ ys_real_module(yang_stmt *ys)
 		clicon_err(OE_YANG, ENOENT, "Belongs-to statement of submodule %s has no argument", yang_argument_get(ym)); /* shouldnt happen */
 		goto done;
 	    }
-	    ym = yang_find_module_by_name(yspec, name);
+	    if ((ym = yang_find_module_by_name(yspec, name)) == NULL)
+		goto done;
 	}
     }
-    return ym;
+    *ymod = ym;
+    retval = 0;
  done:
-    return NULL;
+    return retval;
 }
 
 /*! Find top of tree, the yang specification from within the tree
diff --git a/lib/src/clixon_yang_module.c b/lib/src/clixon_yang_module.c
index 70770bcd..7f7f588b 100644
--- a/lib/src/clixon_yang_module.c
+++ b/lib/src/clixon_yang_module.c
@@ -504,6 +504,7 @@ yang_find_module_by_prefix(yang_stmt *ys,
 	clicon_err(OE_YANG, 0, "My yang spec not found");
 	goto done;
     }
+    /* First try own module */
     if ((my_ymod = ys_module(ys)) == NULL){
 	clicon_err(OE_YANG, 0, "My yang module not found");
 	goto done;
@@ -513,6 +514,7 @@ yang_find_module_by_prefix(yang_stmt *ys,
 	ymod = my_ymod;
 	goto done;
     }
+    /* If no match, try imported modules */
     yimport = NULL;
     while ((yimport = yn_each(my_ymod, yimport)) != NULL) {
 	if (yang_keyword_get(yimport) != Y_IMPORT)
diff --git a/lib/src/clixon_yang_parse_lib.c b/lib/src/clixon_yang_parse_lib.c
index 50b98c49..f0131516 100644
--- a/lib/src/clixon_yang_parse_lib.c
+++ b/lib/src/clixon_yang_parse_lib.c
@@ -353,7 +353,7 @@ yang_expand_grouping(yang_stmt *yn)
 	    do {
 		if (yp == ygrouping){
 
-		    clicon_err(OE_YANG, EFAULT, "Yang use of grouping %s in module %s is defined inside the grouping (recursion)",
+		    clicon_err(OE_YANG, EFAULT, "Yang use of grouping %s in module %s is defined inside the grouping (recursion), see RFC 7950 Sec 7.12: A grouping MUST NOT reference itself",
 			       yang_argument_get(ys),
 			       yang_argument_get(ys_module(yn))
 			       );