diff --git a/CHANGELOG.md b/CHANGELOG.md
index 982c0df5..d31632b5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,17 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## unreleased
 
+### Fixed
+
+ - Mark the following functions with `__attribute__((warn_unused_result))` (when available):
+   - `SmolRTSP_ParseError_print`.
+   - `SmolRTSP_MessageBody_empty`.
+   - `SmolRTSP_Request_uninit`.
+   - `SmolRTSP_Response_uninit`.
+   - `SmolRTSP_NalTransportConfig_default`.
+   - `smolrtsp_determine_start_code`.
+   - `smolrtsp_dgram_socket`.
+
 ## 0.1.0 - 2022-03-30
 
 ### Added
diff --git a/include/smolrtsp/nal.h b/include/smolrtsp/nal.h
index 98f8e1c7..9bd0007b 100644
--- a/include/smolrtsp/nal.h
+++ b/include/smolrtsp/nal.h
@@ -153,7 +153,8 @@ typedef size_t (*SmolRTSP_NalStartCodeTester)(U8Slice99 data);
  * file to #smolrtsp_determine_start_code and invoke the returned tester
  * multiple times afterwards.
  */
-SmolRTSP_NalStartCodeTester smolrtsp_determine_start_code(U8Slice99 data);
+SmolRTSP_NalStartCodeTester
+smolrtsp_determine_start_code(U8Slice99 data) SMOLRTSP_PRIV_MUST_USE;
 
 /**
  * The 3-byte start code tester (`0x000001`).
diff --git a/include/smolrtsp/nal_transport.h b/include/smolrtsp/nal_transport.h
index 97456f99..380e030c 100644
--- a/include/smolrtsp/nal_transport.h
+++ b/include/smolrtsp/nal_transport.h
@@ -52,7 +52,8 @@ typedef struct {
  *  - `max_h264_nalu_size` is #SMOLRTSP_MAX_H264_NALU_SIZE.
  *  - `max_h265_nalu_size` is #SMOLRTSP_MAX_H265_NALU_SIZE.
  */
-SmolRTSP_NalTransportConfig SmolRTSP_NalTransportConfig_default(void);
+SmolRTSP_NalTransportConfig
+SmolRTSP_NalTransportConfig_default(void) SMOLRTSP_PRIV_MUST_USE;
 
 /**
  * An RTP/NAL data transport.
diff --git a/include/smolrtsp/transport.h b/include/smolrtsp/transport.h
index 807559c5..5a20da9e 100644
--- a/include/smolrtsp/transport.h
+++ b/include/smolrtsp/transport.h
@@ -84,7 +84,8 @@ SmolRTSP_Transport smolrtsp_transport_udp(int fd) SMOLRTSP_PRIV_MUST_USE;
  * @return A valid file descriptor or -1 on error (and sets `errno`
  * appropriately).
  */
-int smolrtsp_dgram_socket(int af, const void *restrict addr, uint16_t port);
+int smolrtsp_dgram_socket(int af, const void *restrict addr, uint16_t port)
+    SMOLRTSP_PRIV_MUST_USE;
 
 /**
  * Returns a pointer to the IP address of @p addr.
diff --git a/include/smolrtsp/types/error.h b/include/smolrtsp/types/error.h
index b0f54924..ebab74cd 100644
--- a/include/smolrtsp/types/error.h
+++ b/include/smolrtsp/types/error.h
@@ -84,7 +84,8 @@ datatype99(
  *
  * @pre `w.self && w.vptr`
  */
-int SmolRTSP_ParseError_print(SmolRTSP_ParseError self, SmolRTSP_Writer w);
+int SmolRTSP_ParseError_print(SmolRTSP_ParseError self, SmolRTSP_Writer w)
+    SMOLRTSP_PRIV_MUST_USE;
 
 /**
  * A status of successful parsing.
diff --git a/include/smolrtsp/types/message_body.h b/include/smolrtsp/types/message_body.h
index 33e756bd..a34fbba3 100644
--- a/include/smolrtsp/types/message_body.h
+++ b/include/smolrtsp/types/message_body.h
@@ -30,7 +30,7 @@ SmolRTSP_ParseResult SmolRTSP_MessageBody_parse(
 /**
  * Returns an empty message body.
  */
-SmolRTSP_MessageBody SmolRTSP_MessageBody_empty(void);
+SmolRTSP_MessageBody SmolRTSP_MessageBody_empty(void) SMOLRTSP_PRIV_MUST_USE;
 
 /**
  * Tests @p lhs and @p rhs for equality.
diff --git a/include/smolrtsp/types/request.h b/include/smolrtsp/types/request.h
index 8a0ac141..133533da 100644
--- a/include/smolrtsp/types/request.h
+++ b/include/smolrtsp/types/request.h
@@ -43,7 +43,7 @@ typedef struct {
 /**
  * Returns an RTSP request suitable for being parsed.
  */
-SmolRTSP_Request SmolRTSP_Request_uninit(void);
+SmolRTSP_Request SmolRTSP_Request_uninit(void) SMOLRTSP_PRIV_MUST_USE;
 
 /**
  * Serialises @p self into @p w.
diff --git a/include/smolrtsp/types/response.h b/include/smolrtsp/types/response.h
index e867e140..d23f0ac6 100644
--- a/include/smolrtsp/types/response.h
+++ b/include/smolrtsp/types/response.h
@@ -43,7 +43,7 @@ typedef struct {
 /**
  * Returns an RTSP response suitable for being parsed.
  */
-SmolRTSP_Response SmolRTSP_Response_uninit(void);
+SmolRTSP_Response SmolRTSP_Response_uninit(void) SMOLRTSP_PRIV_MUST_USE;
 
 /**
  * Serialises @p self into @p w.