diff --git a/R/d18O_model.r b/R/d18O_model.r
index eb2741f..e40f21d 100644
--- a/R/d18O_model.r
+++ b/R/d18O_model.r
@@ -58,7 +58,7 @@ d18O_model <- function(SST, # Function that converts SST values into d18O
     if(transfer_function == "KimONeil97"){
         d18Oc <- cbind(SST[,1], (exp((18.03 * 1000 / (SST[,2] + 273.15) - 32.42) / 1000) - 1) * 1000 + (0.97001 * d18Ow - 29.99)) # Use Kim and O'Neil (1997) with conversion between VSMOW and VPDB by Brand et al. (2014) and Kim et al. (2015)
     }else if(transfer_function == "GrossmanKu86"){
-        d18Oc <- cbind(SST[,1], (20.6 - SST[,2]) / 4.34 + d18Ow + 0.2) # Use Grossmann and Ku (1986) modified by Dettmann et al. (1999)
+        d18Oc <- cbind(SST[,1], (20.6 - SST[,2]) / 4.34 + d18Ow - 0.2) # Use Grossmann and Ku (1986) modified by Dettmann et al. (1999)
     }else{
         return("ERROR: Supplied transfer function is not recognized")
     }