diff --git a/CHANGELOG.md b/CHANGELOG.md
index ff2863af..cfa12536 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,6 @@
+Unreleased:
+- fix: RampControl.cpp declared the log2 timer-frequency variables `static`, conflicting with their `extern` declaration in RampGenerator.h. That combination is ill-formed C++ (a static redeclaration cannot follow a non-static/extern one in the same translation unit) and breaks the build for any platform whose TICKS_PER_S isn't exactly 16000000 or 21000000 - e.g. an AVR board not running at 16/21 MHz - the moment SUPPORT_LOG2_TIMER_FREQ_VARIABLES is exercised
+
 1.3.3:
 - moveTimed(0, duration): pause uses last direction XOR prepare_revert (default false does not toggle DIR; true pauses in the opposite direction)
 
diff --git a/src/fas_ramp/RampControl.cpp b/src/fas_ramp/RampControl.cpp
index 800c4fb9..47afc952 100644
--- a/src/fas_ramp/RampControl.cpp
+++ b/src/fas_ramp/RampControl.cpp
@@ -7,9 +7,12 @@
 #include "fas_arch/common.h"
 
 #ifdef SUPPORT_LOG2_TIMER_FREQ_VARIABLES
-static log2_value_t log2_timer_freq;
-static log2_value_t log2_timer_freq_div_sqrt_of_2;
-static log2_value_t log2_timer_freq_square_div_2;
+// Definitions for the `extern` declarations in RampGenerator.h. Must have
+// external linkage (no `static`): RampGenerator.cpp, a separate translation
+// unit, also uses these via the LOG2_TICKS_PER_S* macros in RampCalculator.h.
+log2_value_t log2_timer_freq;
+log2_value_t log2_timer_freq_div_sqrt_of_2;
+log2_value_t log2_timer_freq_square_div_2;
 #endif
 
 void ramp_rw_s::init() {