diff --git a/R/bmerge.R b/R/bmerge.R
index a592f9014..57463b580 100644
--- a/R/bmerge.R
+++ b/R/bmerge.R
@@ -62,19 +62,31 @@ bmerge <- function(i, x, leftcols, rightcols, io, xo, roll, rollends, nomatch, v
             # <OUTDATED> NAs can be produced by this level match, in which case the C code (it knows integer value NA)
             # can skip over the lookup. It's therefore important we pass NA rather than 0 to the C code.
         }
+        # Fix for #1108. 
+        # TODO: clean this code up...
+        # NOTE: bit64::is.double(int64) returns FALSE.. but base::is.double returns TRUE
+        is.int64 <- function(x) inherits(x, 'integer64')
+        is.strictlydouble <- function(x) !is.int64(x) && is.double(x)
         if (is.integer(x[[rc]]) && (is.double(i[[lc]]) || is.logical(i[[lc]]))) {
             # TO DO: add warning if reallyreal about loss of precision
             # or could coerce in binary search on the fly, at cost
             if (verbose) cat("Coercing ", typeof(i[[lc]])," column i.'",icnam,"' to integer to match type of x.'",xcnam,"'. Please avoid coercion for efficiency.\n",sep="")
             newval = i[[lc]]
-            mode(newval) = "integer"  # retains column attributes (such as IDateTime class)
-            set(i,j=lc,value=newval)
-        }
-        if (is.double(x[[rc]]) && (is.integer(i[[lc]]) || is.logical(i[[lc]]))) {
+            if (is.int64(newval))
+                newval = as.integer(newval)
+            else mode(newval) = "integer"  # retains column attributes (such as IDateTime class)
+            set(i, j=lc, value=newval)
+        } else if (is.int64(x[[rc]]) && (is.integer(i[[lc]]) || is.logical(i[[lc]]) || is.strictlydouble(i[[lc]]) )) {
+            if (verbose) cat("Coercing ",typeof(i[[lc]])," column i.'",icnam,"' to double to match type of x.'",xcnam,"'. Please avoid coercion for efficiency.\n",sep="")
+            newval = bit64::as.integer64(i[[lc]])
+            set(i, j=lc, value=newval)
+        } else if (is.strictlydouble(x[[rc]]) && (is.integer(i[[lc]]) || is.logical(i[[lc]]) || is.int64(i[[lc]]) )) {
             if (verbose) cat("Coercing ",typeof(i[[lc]])," column i.'",icnam,"' to double to match type of x.'",xcnam,"'. Please avoid coercion for efficiency.\n",sep="")
             newval = i[[lc]]
-            mode(newval) = "double"
-            set(i,j=lc,value=newval)
+            if (is.int64(newval))
+                newval = as.numeric(newval)
+            else mode(newval) = "double"
+            set(i, j=lc, value=newval)
         }
     }
         
diff --git a/README.md b/README.md
index 912f03ccb..dea10b8cc 100644
--- a/README.md
+++ b/README.md
@@ -184,6 +184,8 @@
 
   47. `as.matrix(DT)` handles cases where `DT` contains both numeric and logical columns correctly (doesn't coerce to character columns anymore). Closes [#1083](https://github.com/Rdatatable/data.table/issues/1083). Thanks to @bramvisser for the [SO post](http://stackoverflow.com/questions/29068328/correlation-between-numeric-and-logical-variable-gives-intended-error).
 
+  48. Coercion is handled properly on subsets/joins on `integer64` key columns. Closes [#1108](https://github.com/Rdatatable/data.table/issues/1108). Thanks to @vspinu.
+
 #### NOTES
 
   1. Clearer explanation of what `duplicated()` does (borrowed from base). Thanks to @matthieugomez for pointing out. Closes [#872](https://github.com/Rdatatable/data.table/issues/872).
diff --git a/inst/tests/tests.Rraw b/inst/tests/tests.Rraw
index 4d7703983..5f10fe64e 100644
--- a/inst/tests/tests.Rraw
+++ b/inst/tests/tests.Rraw
@@ -6292,6 +6292,21 @@ rownames(DF) = sample(letters, 10)
 ans = DF[order(-xtfrm(DF$y), DF$x), ]
 test(1511, ans, setorder(DF, -y, x))
 
+# fix for #1108
+if ("package:bit64" %in% search()) {
+    dt <- data.table(id = as.integer64(1:3), a = c("a", "b", "c"), key = "id")
+    test(1512.1, dt[.(2)], dt[.(as.integer64(2))])
+    test(1512.2, dt[.(2L)], dt[.(as.integer64(2))])
+
+    dt <- data.table(id = as.numeric(1:3), a = c("a", "b", "c"), key = "id")
+    test(1512.3, dt[.(2L)], dt[.(2)])
+    test(1512.4, dt[.(as.integer64(2))], dt[.(2)])
+
+    dt <- data.table(id = 1:3, a = c("a", "b", "c"), key = "id")
+    test(1512.5, dt[.(2)], dt[.(2L)])
+    test(1512.6, dt[.(as.integer64(2))], dt[.(2L)])
+}
+
 ##########################