diff --git a/local.c b/local.c
index 8de198e..e4be12b 100644
--- a/local.c
+++ b/local.c
@@ -382,7 +382,7 @@ LCL_SetAbsoluteFrequency(double afreq_ppm)
   
   afreq_ppm = (*drv_set_freq)(afreq_ppm);
 
-  dfreq = (afreq_ppm - current_freq_ppm) / (1.0e6 + current_freq_ppm);
+  dfreq = (afreq_ppm - current_freq_ppm) / (1.0e6 - current_freq_ppm);
 
   LCL_ReadRawTime(&raw);
   LCL_CookTime(&raw, &cooked, NULL);
@@ -411,11 +411,11 @@ LCL_AccumulateDeltaFrequency(double dfreq)
    are handled in units of ppm, whereas the 'dfreq' argument is in
    terms of the gradient of the (offset) v (local time) function. */
 
-  current_freq_ppm = (1.0 + dfreq) * current_freq_ppm + 1.0e6 * dfreq;
+  current_freq_ppm = (1.0 - dfreq) * current_freq_ppm + 1.0e6 * dfreq;
 
   /* Call the system-specific driver for setting the frequency */
   current_freq_ppm = (*drv_set_freq)(current_freq_ppm);
-  dfreq = (current_freq_ppm - old_freq_ppm) / (1.0e6 + old_freq_ppm);
+  dfreq = (current_freq_ppm - old_freq_ppm) / (1.0e6 - old_freq_ppm);
 
   LCL_ReadRawTime(&raw);
   LCL_CookTime(&raw, &cooked, NULL);
@@ -508,14 +508,14 @@ LCL_AccumulateFrequencyAndOffset(double dfreq, double doffset, double corr_rate)
   /* Work out new absolute frequency.  Note that absolute frequencies
    are handled in units of ppm, whereas the 'dfreq' argument is in
    terms of the gradient of the (offset) v (local time) function. */
-  current_freq_ppm = (1.0 + dfreq) * old_freq_ppm + 1.0e6 * dfreq;
+  current_freq_ppm = (1.0 - dfreq) * old_freq_ppm + 1.0e6 * dfreq;
 
   DEBUG_LOG(LOGF_Local, "old_freq=%.3fppm new_freq=%.3fppm offset=%.6fsec",
       old_freq_ppm, current_freq_ppm, doffset);
 
   /* Call the system-specific driver for setting the frequency */
   current_freq_ppm = (*drv_set_freq)(current_freq_ppm);
-  dfreq = (current_freq_ppm - old_freq_ppm) / (1.0e6 + old_freq_ppm);
+  dfreq = (current_freq_ppm - old_freq_ppm) / (1.0e6 - old_freq_ppm);
 
   (*drv_accrue_offset)(doffset, corr_rate);
 
diff --git a/rtc_linux.c b/rtc_linux.c
index fe52c33..3fcf297 100644
--- a/rtc_linux.c
+++ b/rtc_linux.c
@@ -282,7 +282,7 @@ slew_samples
 
   if (coefs_valid) {
     coef_seconds_fast += doffset;
-    coef_gain_rate = (1.0 + dfreq) * (1.0 + coef_gain_rate) - 1.0;
+    coef_gain_rate = (1.0 - dfreq) * coef_gain_rate + dfreq;
   }
 
   DEBUG_LOG(LOGF_RtcLinux, "dfreq=%.8f doffset=%.6f old_fast=%.6f old_rate=%.3f new_fast=%.6f new_rate=%.3f",