diff --git a/git-flow b/git-flow
index b34c31e..ca72cde 100755
--- a/git-flow
+++ b/git-flow
@@ -357,8 +357,16 @@ def tag_command():
     until_dash = last_version.index("-") if "-" in last_version else None
     [major, minor, patch] = map(int, last_version[from_major:until_dash].split("."))
 
-    merged_branch_type = merged_branch[:merged_branch.index('/')] if '/' in merged_branch else merged_branch
-    increment = BRANCH_TYPES_INCREMENT[merged_branch_type]
+    components = merged_branch.split("/")
+
+    if len(components) not in [2, 4]:
+        raise RuntimeError("Branch mergeado es inválido: " + merged_branch)
+    elif len(components) == 4 and components[0] != "release":
+        raise RuntimeError("Release branch mergeado es inválido: " + merged_branch)
+    elif components[-2] not in BRANCH_TYPES:
+        raise RuntimeError("Tipo de rama mergeado es inválido: " + components[-2])
+
+    increment = BRANCH_TYPES_INCREMENT[components[-2]]
 
     if increment == "major":
         major = major + 1