diff --git a/libavutil/avstring.c b/libavutil/avstring.c
index 24d1bb98e9..57fe74d252 100644
--- a/libavutil/avstring.c
+++ b/libavutil/avstring.c
@@ -317,28 +317,6 @@ int av_escape(char **dst, const char *src, const char *special_chars,
     }
 }
 
-int av_isdigit(int c)
-{
-    return c >= '0' && c <= '9';
-}
-
-int av_isgraph(int c)
-{
-    return c > 32 && c < 127;
-}
-
-int av_isspace(int c)
-{
-    return c == ' ' || c == '\f' || c == '\n' || c == '\r' || c == '\t' ||
-           c == '\v';
-}
-
-int av_isxdigit(int c)
-{
-    c = av_tolower(c);
-    return av_isdigit(c) || (c >= 'a' && c <= 'f');
-}
-
 int av_match_name(const char *name, const char *names)
 {
     const char *p;
diff --git a/libavutil/avstring.h b/libavutil/avstring.h
index 234c03078b..a306e8974d 100644
--- a/libavutil/avstring.h
+++ b/libavutil/avstring.h
@@ -203,17 +203,27 @@ char *av_strtok(char *s, const char *delim, char **saveptr);
 /**
  * Locale-independent conversion of ASCII isdigit.
  */
-av_const int av_isdigit(int c);
+static inline av_const int av_isdigit(int c)
+{
+    return c >= '0' && c <= '9';
+}
 
 /**
  * Locale-independent conversion of ASCII isgraph.
  */
-av_const int av_isgraph(int c);
+static inline av_const int av_isgraph(int c)
+{
+    return c > 32 && c < 127;
+}
 
 /**
  * Locale-independent conversion of ASCII isspace.
  */
-av_const int av_isspace(int c);
+static inline av_const int av_isspace(int c)
+{
+    return c == ' ' || c == '\f' || c == '\n' || c == '\r' || c == '\t' ||
+           c == '\v';
+}
 
 /**
  * Locale-independent conversion of ASCII characters to uppercase.
@@ -238,7 +248,11 @@ static inline av_const int av_tolower(int c)
 /**
  * Locale-independent conversion of ASCII isxdigit.
  */
-av_const int av_isxdigit(int c);
+static inline av_const int av_isxdigit(int c)
+{
+    c = av_tolower(c);
+    return av_isdigit(c) || (c >= 'a' && c <= 'f');
+}
 
 /**
  * Locale-independent case-insensitive compare.