diff --git a/zathura/content-type.c b/zathura/content-type.c
index 9352da1..3440973 100644
--- a/zathura/content-type.c
+++ b/zathura/content-type.c
@@ -82,7 +82,7 @@ zathura_content_type_free(zathura_content_type_context_t* context)
 static const size_t GT_MAX_READ = 1 << 16;
 
 #ifdef WITH_MAGIC
-static const char*
+static char*
 guess_type_magic(zathura_content_type_context_t* context, const char* path)
 {
   if (context == NULL || context->magic == NULL) {
@@ -97,15 +97,13 @@ guess_type_magic(zathura_content_type_context_t* context, const char* path)
     girara_debug("failed guessing filetype: %s", magic_error(context->magic));
     return NULL;
   }
-  /* dup so we own the memory */
-  mime_type = g_strdup(mime_type);
-
   girara_debug("magic detected filetype: %s", mime_type);
 
-  return mime_type;
+  /* dup so we own the memory */
+  return g_strdup(mime_type);;
 }
 
-static const char*
+static char*
 guess_type_file(const char* UNUSED(path))
 {
   return NULL;
@@ -118,7 +116,7 @@ guess_type_magic(zathura_content_type_context_t* UNUSED(context),
   return NULL;
 }
 
-static const char*
+static char*
 guess_type_file(const char* path)
 {
   GString* command = g_string_new("file -b --mime-type ");
@@ -149,11 +147,11 @@ guess_type_file(const char* path)
 }
 #endif
 
-static const char*
+static char*
 guess_type_glib(const char* path)
 {
   gboolean uncertain = FALSE;
-  const char* content_type = g_content_type_guess(path, NULL, 0, &uncertain);
+  char* content_type = g_content_type_guess(path, NULL, 0, &uncertain);
   if (content_type == NULL) {
     girara_debug("g_content_type failed\n");
   } else {
@@ -203,12 +201,12 @@ guess_type_glib(const char* path)
   return NULL;
 }
 
-const char*
+char*
 zathura_content_type_guess(zathura_content_type_context_t* context,
                            const char* path)
 {
   /* try libmagic first */
-  const char* content_type = guess_type_magic(context, path);
+  char* content_type = guess_type_magic(context, path);
   if (content_type != NULL) {
     return content_type;
   }
diff --git a/zathura/content-type.h b/zathura/content-type.h
index c02d937..9bd367d 100644
--- a/zathura/content-type.h
+++ b/zathura/content-type.h
@@ -24,9 +24,9 @@ void zathura_content_type_free(zathura_content_type_context_t* context);
  * the available libraries.
  *
  * @param path file name
- * @return content type of path
+ * @return content type of path, needs to freeed with g_free.
  */
-const char* zathura_content_type_guess(zathura_content_type_context_t* context,
-                                       const char* path);
+char* zathura_content_type_guess(zathura_content_type_context_t* context,
+                                 const char* path);
 
 #endif
diff --git a/zathura/document.c b/zathura/document.c
index f4563b7..7ed9acb 100644
--- a/zathura/document.c
+++ b/zathura/document.c
@@ -70,7 +70,7 @@ zathura_document_open(zathura_t* zathura, const char* path, const char* uri,
 
   GFile* file = g_file_new_for_path(path);
   char* real_path = NULL;
-  const char* content_type = NULL;
+  char* content_type = NULL;
   zathura_plugin_t* plugin = NULL;
   zathura_document_t* document = NULL;
 
@@ -106,7 +106,7 @@ zathura_document_open(zathura_t* zathura, const char* path, const char* uri,
     goto error_free;
   }
 
-  g_free((void*)content_type);
+  g_free(content_type);
   content_type = NULL;
 
   document = g_try_malloc0(sizeof(zathura_document_t));
diff --git a/zathura/utils.c b/zathura/utils.c
index ea5bc2b..d99a461 100644
--- a/zathura/utils.c
+++ b/zathura/utils.c
@@ -52,15 +52,13 @@ file_valid_extension(zathura_t* zathura, const char* path)
     return false;
   }
 
-  const gchar* content_type =
-    zathura_content_type_guess(zathura->content_type_context, path);
+  char* content_type = zathura_content_type_guess(zathura->content_type_context, path);
   if (content_type == NULL) {
     return false;
   }
 
-  zathura_plugin_t* plugin =
-    zathura_plugin_manager_get_plugin(zathura->plugins.manager, content_type);
-  g_free((void*)content_type);
+  zathura_plugin_t* plugin = zathura_plugin_manager_get_plugin(zathura->plugins.manager, content_type);
+  g_free(content_type);
 
   return (plugin == NULL) ? false : true;
 }