diff --git a/dynstr.c b/dynstr.c
index 2455031..e9ef185 100644
--- a/dynstr.c
+++ b/dynstr.c
@@ -30,33 +30,34 @@ void dynstr_init(struct dynstr *const d)
     memset(d, 0, sizeof *d);
 }
 
+enum dynstr_err dynstr_vappend(struct dynstr *const d, const char *const format, va_list ap)
+{
+    enum dynstr_err err = DYNSTR_OK;
+    const size_t src_len = vsnprintf(NULL, 0, format, ap);
+    const size_t new_len = d->len + src_len + 1;
+
+    d->str = realloc(d->str, new_len * sizeof *d->str);
+
+    if (d->str)
+    {
+        vsprintf(d->str + d->len, format, ap);
+        d->len += src_len;
+    }
+    else
+    {
+        err = DYNSTR_ERR_ALLOC;
+    }
+
+    va_end(ap);
+    return err;
+}
+
 enum dynstr_err dynstr_append(struct dynstr *const d, const char *const format, ...)
 {
     va_list ap;
 
     va_start(ap, format);
-
-    {
-        const size_t src_len = vsnprintf(NULL, 0, format, ap);
-        const size_t new_len = d->len + src_len + 1;
-        va_end(ap);
-
-        d->str = realloc(d->str, new_len * sizeof *d->str);
-
-        if (d->str)
-        {
-            va_start(ap, format);
-            vsprintf(d->str + d->len, format, ap);
-            va_end(ap);
-            d->len += src_len;
-        }
-        else
-        {
-            return DYNSTR_ERR_ALLOC;
-        }
-    }
-
-    return DYNSTR_OK;
+    return dynstr_vappend(d, format, ap);
 }
 
 enum dynstr_err dynstr_prepend(struct dynstr *const d, const char *const format, ...)
diff --git a/include/dynstr.h b/include/dynstr.h
index 925423a..2c36865 100644
--- a/include/dynstr.h
+++ b/include/dynstr.h
@@ -21,6 +21,7 @@
 #error C99 support is mandatory for dynstr
 #endif /* __STDC_VERSION < 199901L */
 
+#include <stdarg.h>
 #include <stddef.h>
 #include <stdbool.h>
 
@@ -108,6 +109,19 @@ void dynstr_init(struct dynstr *d);
  */
 enum dynstr_err dynstr_append(struct dynstr *d, const char *format, ...);
 
+/**
+ * This function takes a string literal in printf format and a variable
+ * argument list, calculates its size and concatenates it into the
+ * dynamic string.
+ * @param d Dynamic string where new string will be appended.
+ * @param format String literal in printf format.
+ * @param ap Variable argument list.
+ * @return Returns one of the following error codes:
+ *    # DYNSTR_OK if successful.
+ *    # DYNSTR_ERR_ALLOC if no more memory is available.
+ */
+enum dynstr_err dynstr_vappend(struct dynstr *d, const char *format, va_list ap);
+
 /**
  * This function takes a string literal in printf format and a variable
  * number of arguments, calculates its size and prepends it into the