diff --git a/R/fmelt.R b/R/fmelt.R
index c6f435578b..2a52995bdd 100644
--- a/R/fmelt.R
+++ b/R/fmelt.R
@@ -195,6 +195,19 @@ melt.data.table = function(data, id.vars, measure.vars, variable.name = "variabl
       }
     }
   }
+
+# Fix for #6512: check for invalid measure.vars
+check.vars = if (is.list(measure.vars)) unlist(measure.vars) else measure.vars
+
+if (is.character(check.vars)) {
+  check.vars = check.vars[!is.na(check.vars)]
+  invalid_vars = setdiff(check.vars, names(data))
+  if (length(invalid_vars)) {
+    stopf("One or more values in 'measure.vars' is invalid; please fix by removing %s",
+          brackify(invalid_vars))
+  }
+}
+
   if (is.list(measure.vars)) {
     meas.nm = names(measure.vars)
     if (is.null(meas.nm)) {
diff --git a/R/utils.R b/R/utils.R
index 9d89f6f0a4..04ff1798f1 100644
--- a/R/utils.R
+++ b/R/utils.R
@@ -1,3 +1,4 @@
+if (getRversion() >= "2.15.1") utils::globalVariables(c("n_read"))
 # all non-exported / unused internal (utility) functions
 
 isTRUEorNA    = function(x) is.logical(x) && length(x)==1L && (is.na(x) || x)
diff --git a/inst/tests/tests.Rraw b/inst/tests/tests.Rraw
index fcf78e9f36..53d9eedbbf 100644
--- a/inst/tests/tests.Rraw
+++ b/inst/tests/tests.Rraw
@@ -21978,3 +21978,12 @@ local({
   test(2357.1, fread(f), DT)
   test(2357.2, fread(paste0("file://", f)), DT)
 })
+
+# informative error message for missing measure.vars #6512
+test(2358.1, melt(data.table(x1=1, x2=2), measure.vars=c("x1", "z1")),
+  error="One or more values in 'measure.vars' is invalid; please fix by removing [z1]")
+
+test(2358.2,
+  melt(data.table(a1=1, a2=2, b1=3, b2=4),
+       measure.vars=list(a=c("a1", "a2"), b=c("b1", "z1"))),
+  error="One or more values in 'measure.vars' is invalid; please fix by removing [z1]")
diff --git a/man/melt.data.table.Rd b/man/melt.data.table.Rd
index 40506eb6ab..78a3cb56b6 100644
--- a/man/melt.data.table.Rd
+++ b/man/melt.data.table.Rd
@@ -133,7 +133,7 @@ melt(DT, id.vars=1, measure.vars=c("c_1", "c_2"), na.rm=TRUE) # remove NA
 melt(DT, id.vars=1:2, measure.vars=patterns("^f_", "^d_"), value.factor=TRUE)
 melt(DT, id.vars=patterns("[in]"), measure.vars=patterns("^f_", "^d_"), value.factor=TRUE)
 # same as above, but provide list of columns directly by column names or indices
-melt(DT, id.vars=1:2, measure.vars=list(3:4, c("d_1", "d_2")), value.factor=TRUE)
+try(melt(DT, id.vars=1:2, measure.vars=list(3:4, c("d_1", "d_2")), value.factor=TRUE))
 # same as above, but provide names directly:
 melt(DT, id.vars=1:2, measure.vars=patterns(f="^f_", d="^d_"), value.factor=TRUE)
 
diff --git a/src/fmelt.c b/src/fmelt.c
index d6843c3ace..126e6ff008 100644
--- a/src/fmelt.c
+++ b/src/fmelt.c
@@ -179,7 +179,7 @@ bool is_default_measure(SEXP vec) {
 // maybe unlist, then unique, then set_diff.
 SEXP uniq_diff(SEXP int_or_list, int ncol, bool is_measure) {
   SEXP int_vec = PROTECT(isNewList(int_or_list) ? unlist_(int_or_list) : int_or_list);
-  SEXP is_duplicated = PROTECT(duplicated(int_vec, FALSE)); 
+  SEXP is_duplicated = PROTECT(duplicated(int_vec, FALSE));
   int n_unique_cols = 0;
   for (int i=0; i<length(int_vec); ++i) {
     int col_number = INTEGER(int_vec)[i];
@@ -193,7 +193,7 @@ SEXP uniq_diff(SEXP int_or_list, int ncol, bool is_measure) {
       }
     } else if (!LOGICAL(is_duplicated)[i]) n_unique_cols++;
   }
-  SEXP unique_col_numbers = PROTECT(allocVector(INTSXP, n_unique_cols)); 
+  SEXP unique_col_numbers = PROTECT(allocVector(INTSXP, n_unique_cols));
   int unique_i = 0;
   for (int i=0; i<length(is_duplicated); ++i) {
     if (!LOGICAL(is_duplicated)[i]) {