diff --git a/Marlin/src/core/serial.cpp b/Marlin/src/core/serial.cpp
index 727b191d04044..64704c1e6cb42 100644
--- a/Marlin/src/core/serial.cpp
+++ b/Marlin/src/core/serial.cpp
@@ -85,11 +85,6 @@ void serial_offset(const_float_t v, const uint8_t sp/*=0*/) {
   SERIAL_DECIMAL(v);
 }
 
-void serial_ternary(const bool onoff, FSTR_P const pre, FSTR_P const on, FSTR_P const off, FSTR_P const post/*=nullptr*/) {
-  if (pre) serial_print(pre);
-  serial_print(onoff ? on : off);
-  if (post) serial_print(post);
-}
 void serialprint_onoff(const bool onoff) { serial_print(onoff ? F(STR_ON) : F(STR_OFF)); }
 void serialprintln_onoff(const bool onoff) { serialprint_onoff(onoff); SERIAL_EOL(); }
 void serialprint_truefalse(const bool tf) { serial_print(tf ? F("true") : F("false")); }
diff --git a/Marlin/src/core/serial.h b/Marlin/src/core/serial.h
index a1126d74615c5..a741d4b1e4d0e 100644
--- a/Marlin/src/core/serial.h
+++ b/Marlin/src/core/serial.h
@@ -327,7 +327,12 @@ inline void serial_echolnpair(FSTR_P const fstr, T v) { serial_echolnpair_P(FTOP
 
 void serial_echo_start();
 void serial_error_start();
-void serial_ternary(const bool onoff, FSTR_P const pre, FSTR_P const on, FSTR_P const off, FSTR_P const post=nullptr);
+inline void serial_ternary(const bool onoff, FSTR_P const pre, FSTR_P const on, FSTR_P const off, FSTR_P const post=nullptr) {
+  if (pre) serial_print(pre);
+  if (onoff && on) serial_print(on);
+  if (!onoff && off) serial_print(off);
+  if (post) serial_print(post);
+}
 void serialprint_onoff(const bool onoff);
 void serialprintln_onoff(const bool onoff);
 void serialprint_truefalse(const bool tf);
diff --git a/Marlin/src/module/temperature.cpp b/Marlin/src/module/temperature.cpp
index 1aeec1c23d7fc..cb063332c5b46 100644
--- a/Marlin/src/module/temperature.cpp
+++ b/Marlin/src/module/temperature.cpp
@@ -2979,7 +2979,7 @@ void Temperature::init() {
             if (ENABLED(REPORT_ADAPTIVE_FAN_SLOWING) && DEBUGGING(INFO)) {
               const uint8_t fss7 = fan_speed_scaler[fan_index] & 0x80;
               if (fss7 ^ (scale & 0x80))
-                SERIAL_ECHO_TERNARY(fss7, "Adaptive Fan Slowing ", "", "de", "activated.\n");
+                serial_ternary(fss7, F("Adaptive Fan Slowing "), nullptr, F("de"), F("activated.\n"));
             }
 
             fan_speed_scaler[fan_index] = scale;