diff --git a/doc/rst/source/mapproject.rst b/doc/rst/source/mapproject.rst
index 92093c2df4a..3c9c3ccbdce 100644
--- a/doc/rst/source/mapproject.rst
+++ b/doc/rst/source/mapproject.rst
@@ -15,7 +15,7 @@ Synopsis
 **gmt mapproject** [ *tables* ] |-J|\ *parameters*
 |SYN_OPT-R|
 [ |-A|\ **b**\|\ **B**\|\ **f**\|\ **F**\|\ **o**\|\ **O**\ [*lon0*/*lat0*][**+v**] ]
-[ |-C|\ [*dx*/*dy*] ]
+[ |-C|\ [*dx*/*dy*][**+m**] ]
 [ |-D|\ **c**\|\ **i**\|\ **p** ]
 [ |-E|\ [*datum*] ] [ |-F|\ [*unit*] ]
 [ |-G|\ [*lon0*/*lat0*][**+a**][**+i**][**+u**\ *unit*][**+v**] ]
@@ -105,7 +105,7 @@ Optional Arguments
 
 .. _-C:
 
-**-C**\ [*dx*/*dy*]
+**-C**\ [*dx*/*dy*][**+m**]
     Set center of projected coordinates to be at map projection center
     [Default is lower left corner]. Optionally, add offsets in the
     projected units to be added (or subtracted when **-I** is set) to
@@ -113,7 +113,9 @@ Optional Arguments
     northings for particular projection zones [0/0]. The unit used for
     the offsets is the plot distance unit in effect (see
     :term:`PROJ_LENGTH_UNIT`) unless **-F** is used, in which case the
-    offsets are in meters.
+    offsets are in meters.  Alternatively, for the Mercator projection
+    only, append **+m** to set the origin of the projected *y* coordinates
+    to coincide with the standard parallel [Equator].
 
 .. _-D:
 
diff --git a/src/gmt_init.c b/src/gmt_init.c
index b596cd32efd..d08b6ea6e5c 100644
--- a/src/gmt_init.c
+++ b/src/gmt_init.c
@@ -865,7 +865,7 @@ GMT_LOCAL int gmtinit_rectR_to_geoR (struct GMT_CTRL *GMT, char unit, double rec
 	uint64_t dim[GMT_DIM_SIZE] = {1, 1, 2, 2};	/* Just a single data table with one segment with two 2-column records */
 	bool was_R, was_J;
 	double wesn[4];
-	char buffer[GMT_LEN256] = {""}, Jstring[GMT_LEN128] = {""}, in_string[GMT_VF_LEN] = {""}, out_string[GMT_VF_LEN] = {""}, *v = NULL;
+	char buffer[GMT_LEN256] = {""}, Jstring[GMT_LEN128] = {""}, in_string[GMT_VF_LEN] = {""}, out_string[GMT_VF_LEN] = {""}, origin_flag[4] = {""}, *v = NULL;
 	struct GMT_DATASET *In = NULL, *Out = NULL;
 
 	GMT_Report (GMT->parent, GMT_MSG_DEBUG, "Call gmtinit_rectR_to_geoR to convert projected -R to geo -R\n");
@@ -911,6 +911,8 @@ GMT_LOCAL int gmtinit_rectR_to_geoR (struct GMT_CTRL *GMT, char unit, double rec
 				GMT_Report (GMT->parent, GMT_MSG_ERROR, "UTM projection insufficiently specified to auto-determine geographic region\n");
 				return (GMT_MAP_NO_PROJECTION);
 			}
+			if (GMT->current.proj.projection_GMT == GMT_MERCATOR)	/* Special use of Mercator units relative to stated origin */
+				strcpy (origin_flag, "+m");
 			break;
 		case 2: /* Conical: Use default patch */
 			break;
@@ -948,8 +950,8 @@ GMT_LOCAL int gmtinit_rectR_to_geoR (struct GMT_CTRL *GMT, char unit, double rec
 				v[0] = '\0';
 		}
 	}
-	snprintf (buffer, GMT_LEN256, "-R%g/%g/%g/%g -J%s -I -F%c -C -bi2d -bo2d -<%s ->%s --GMT_HISTORY=readonly",
-		wesn[XLO], wesn[XHI], wesn[YLO], wesn[YHI], Jstring, unit, in_string, out_string);
+	snprintf (buffer, GMT_LEN256, "-R%g/%g/%g/%g -J%s -I -F%c -C%s -bi2d -bo2d -<%s ->%s --GMT_HISTORY=readonly",
+		wesn[XLO], wesn[XHI], wesn[YLO], wesn[YHI], Jstring, unit, origin_flag, in_string, out_string);
 	if (get_R) GMT_Report (GMT->parent, GMT_MSG_DEBUG, "Obtaining geographic corner coordinates via mapproject %s\n", buffer);
 	if (GMT_Call_Module (GMT->parent, "mapproject", GMT_MODULE_CMD, buffer) != GMT_OK)	/* Get the corners in degrees via mapproject */
 		return (GMT->parent->error);
diff --git a/src/gmt_proj.c b/src/gmt_proj.c
index fc26d32253c..66aebc66011 100644
--- a/src/gmt_proj.c
+++ b/src/gmt_proj.c
@@ -652,15 +652,17 @@ GMT_LOCAL void gmtproj_ipolar (struct GMT_CTRL *GMT, double *x, double *y, doubl
 
 /* -JM MERCATOR PROJECTION */
 
-GMT_LOCAL void gmtproj_vmerc (struct GMT_CTRL *GMT, double lon0, double slat) {
+GMT_LOCAL void gmtproj_vmerc (struct GMT_CTRL *GMT, double lon0, double lat0) {
 	/* Set up a Mercator transformation with origin at (lon0, lat0) */
 
-	if (GMT->current.proj.GMT_convert_latitudes) slat = gmt_M_latg_to_latc (GMT, slat);
+	double aux_lat0 = (GMT->current.proj.GMT_convert_latitudes) ? gmt_M_latg_to_latc (GMT, lat0) : lat0;
 
 	GMT->current.proj.central_meridian = lon0;
-	GMT->current.proj.j_x = cosd (slat) / d_sqrt (1.0 - GMT->current.proj.ECC2 * sind (slat) * sind (slat)) * GMT->current.proj.EQ_RAD;
+	/* Need geodetic latitude in this expression: */
+	GMT->current.proj.j_x = cosd (lat0) / d_sqrt (1.0 - GMT->current.proj.ECC2 * sind (lat0) * sind (lat0)) * GMT->current.proj.EQ_RAD;
 	GMT->current.proj.j_ix = 1.0 / GMT->current.proj.j_x;
-	GMT->current.proj.j_yc = (fabs (slat) > 0.0) ? GMT->current.proj.j_x * d_log (GMT, tand (45.0 + 0.5 * slat)) : 0.0;
+	/* Need conformal latitude in this expression (same as in gmtproj_merc_sph) */
+	GMT->current.proj.j_yc = (fabs (lat0) > 0.0) ? GMT->current.proj.j_x * d_log (GMT, tand (45.0 + 0.5 * aux_lat0)) : 0.0;
 }
 
 /* Mercator projection for the sphere */
@@ -672,14 +674,14 @@ GMT_LOCAL void gmtproj_merc_sph (struct GMT_CTRL *GMT, double lon, double lat, d
 	if (GMT->current.proj.GMT_convert_latitudes) lat = gmt_M_latg_to_latc (GMT, lat);
 
 	*x = GMT->current.proj.j_x * D2R * lon;
-	*y = (fabs (lat) < 90.0) ? GMT->current.proj.j_x * d_log (GMT, tand (45.0 + 0.5 * lat)) - GMT->current.proj.j_yc : copysign (DBL_MAX, lat);
+	*y = (fabs (lat) < 90.0) ? GMT->current.proj.j_x * d_log (GMT, tand (45.0 + 0.5 * lat)) : copysign (DBL_MAX, lat);
 }
 
 GMT_LOCAL void gmtproj_imerc_sph (struct GMT_CTRL *GMT, double *lon, double *lat, double x, double y) {
 	/* Convert Mercator x/y to lon/lat  (GMT->current.proj.EQ_RAD in GMT->current.proj.j_ix) */
 
 	*lon = x * GMT->current.proj.j_ix * R2D + GMT->current.proj.central_meridian;
-	*lat = atand (sinh ((y + GMT->current.proj.j_yc) * GMT->current.proj.j_ix));
+	*lat = atand (sinh (y * GMT->current.proj.j_ix));
 	if (GMT->current.proj.GMT_convert_latitudes) *lat = gmt_M_latc_to_latg (GMT, *lat);
 }
 
diff --git a/src/mapproject.c b/src/mapproject.c
index c54b3938696..7429eb67447 100644
--- a/src/mapproject.c
+++ b/src/mapproject.c
@@ -97,9 +97,10 @@ struct MAPPROJECT_CTRL {	/* All control options for this program (except common
 		unsigned int mode;
 		double lon, lat;	/* Fixed point of reference */
 	} A;
-	struct MAPPROJECT_C {	/* -C[<false_easting>/<false_northing>] */
+	struct MAPPROJECT_C {	/* -C[<false_easting>/<false_northing>][+m] */
 		bool active;
 		bool shift;
+		bool m_origin;	/* True if we want projected Mercator y-values relative to standard latitude [Equator] */
 		double easting, northing;	/* Shifts */
 	} C;
 	struct MAPPROJECT_D {	/* -D<c|i|p> */
@@ -189,7 +190,7 @@ static int usage (struct GMTAPI_CTRL *API, int level) {
 	const char *name = gmt_show_name_and_purpose (API, THIS_MODULE_LIB, THIS_MODULE_CLASSIC_NAME, THIS_MODULE_PURPOSE);
 	if (level == GMT_MODULE_PURPOSE) return (GMT_NOERROR);
 	GMT_Message (API, GMT_TIME_NONE, "usage: %s <table> %s %s\n", name, GMT_J_OPT, GMT_Rgeo_OPT);
-	GMT_Message (API, GMT_TIME_NONE, "\t[-Ab|B|f|F|o|O[<lon0>/<lat0>][+v]] [-C[<dx></dy>]] [-D%s] [-E[<datum>]] [-F[<unit>]]\n\t[-G[<lon0>/<lat0>][+a][+i][+u<unit>][+v]]", GMT_DIM_UNITS_DISPLAY);
+	GMT_Message (API, GMT_TIME_NONE, "\t[-Ab|B|f|F|o|O[<lon0>/<lat0>][+v]] [-C[<dx></dy>][+m]] [-D%s] [-E[<datum>]] [-F[<unit>]]\n\t[-G[<lon0>/<lat0>][+a][+i][+u<unit>][+v]]", GMT_DIM_UNITS_DISPLAY);
 	GMT_Message (API, GMT_TIME_NONE, " [-I] [-L<table>[+u<unit>][+p]] [-N[a|c|g|m]]\n\t[-Q[e|d]] [-S] [-T[h]<from>[/<to>] [%s] [-W[g|h|j|n|w|x]] [-Z[<speed>][+a][+i][+f][+t<epoch>]]\n", GMT_V_OPT);
 	GMT_Message (API, GMT_TIME_NONE, "\t[%s] [%s] [%s] [%s]\n\t[%s] [%s]\n\t[%s] [%s] [%s]\n\t[%s]\n\t[%s] [%s] [%s] [%s]\n\n",
 		GMT_b_OPT, GMT_d_OPT, GMT_e_OPT, GMT_f_OPT, GMT_g_OPT, GMT_h_OPT, GMT_i_OPT, GMT_j_OPT, GMT_o_OPT, GMT_p_OPT, GMT_q_OPT, GMT_s_OPT, GMT_colon_OPT, GMT_PAR_OPT);
@@ -209,6 +210,7 @@ static int usage (struct GMTAPI_CTRL *API, int level) {
 	GMT_Message (API, GMT_TIME_NONE, "\t-C Return x/y relative to projection center [Default is relative to lower left corner].\n");
 	GMT_Message (API, GMT_TIME_NONE, "\t   Optionally append <dx></dy> to add (or subtract if -I) (i.e., false easting & northing) [0/0].\n");
 	GMT_Message (API, GMT_TIME_NONE, "\t   Units are plot units unless -F is set in which case the unit is meters.\n");
+	GMT_Message (API, GMT_TIME_NONE, "\t   Mercator only: Append +m to set origin for projected y-values to the standard parallel [Equator].\n");
 	GMT_Message (API, GMT_TIME_NONE, "\t-D Temporarily reset PROJ_LENGTH_UNIT to be c (cm), i (inch), or p (point).\n");
 	GMT_Message (API, GMT_TIME_NONE, "\t   Cannot be used if -F is set.\n");
 	GMT_Message (API, GMT_TIME_NONE, "\t-E Convert (lon, lat, h) to Earth Centered Earth Fixed (ECEF) coordinates [-I for inverse].\n");
@@ -482,12 +484,17 @@ static int parse (struct GMT_CTRL *GMT, struct MAPPROJECT_CTRL *Ctrl, struct GMT
 				break;
 			case 'C':
 				Ctrl->C.active = true;
+				if (opt->arg[0] && (p = strstr (opt->arg, "+m"))) {	/* Gave +m for reset relative offsets to Mercator origin */
+					Ctrl->C.m_origin = true;
+					p[0] = '\0';	/* Temporarily chop off modifier */
+				}
 				if (opt->arg[0]) {	/* Also gave shifts */
 					n_errors += gmt_M_check_condition (GMT, sscanf (opt->arg, "%lf/%lf", &Ctrl->C.easting, &Ctrl->C.northing) != 2,
 					                                 "Option -C: Expected -C[<false_easting>/<false_northing>]\n");
 					Ctrl->C.shift = true;
 				}
 				will_need_RJ = true;	/* Since -C is used with projections only */
+				if (p) p[0] = '+';	/* Restore modifier */
 				break;
 			case 'D':
 				Ctrl->D.active = true;
@@ -752,6 +759,8 @@ static int parse (struct GMT_CTRL *GMT, struct MAPPROJECT_CTRL *Ctrl, struct GMT
 	n_errors += gmt_M_check_condition (GMT, ((Ctrl->T.active && GMT->current.proj.datum.h_given) || Ctrl->E.active) &&
 	                                   GMT->common.b.active[GMT_IN] && gmt_get_cols (GMT, GMT_IN) < 3,
 	                                   "For -E or -T, binary input data (-bi) must have at least 3 columns\n");
+	n_errors += gmt_M_check_condition (GMT, Ctrl->C.m_origin && GMT->current.proj.projection_GMT != GMT_MERCATOR, "Option -C: Can only give +m for Mercator projection\n");
+	n_errors += gmt_M_check_condition (GMT, Ctrl->C.m_origin && Ctrl->C.northing != 0.0, "Option -C: Cannot mix +m and the \"northing\" setting\n");
 
 	if (!(n_errors || GMT->common.R.active[RSET])) {
 		GMT->common.R.wesn[XLO] = 0.0;	GMT->common.R.wesn[XHI] = 360.0;
@@ -777,7 +786,7 @@ EXTERN_MSC int GMT_mapproject (void *V_API, int mode, void *args) {
 	uint64_t row, n_read_in_seg, seg, n_read = 0, n = 0, k, n_output = 0;
 
 	double x_in = 0.0, y_in = 0.0, d = 0.0, fwd_scale, inv_scale, xtmp, ytmp, *out = NULL;
-	double xmin, xmax, ymin, ymax, inch_to_unit, unit_to_inch, u_scale, y_out_min;
+	double xmin, xmax, ymin, ymax, inch_to_unit, unit_to_inch, u_scale, y_out_min, m_standard_y_value = 0.0;
 	double x_in_min, x_in_max, y_in_min, y_in_max, x_out_min, x_out_max, y_out_max;
 	double xnear = 0.0, ynear = 0.0, lon_prev = 0, lat_prev = 0, **data = NULL, *in = NULL;
 	double speed = 0, last_speed = -1.0, extra[MP_COL_N];	/* Max possible extra output columns from -A -G -L -Z */
@@ -1163,9 +1172,14 @@ EXTERN_MSC int GMT_mapproject (void *V_API, int mode, void *args) {
 	two = (Ctrl->E.active || (Ctrl->T.active && GMT->current.proj.datum.h_given)) ? 3 : 2;	/* # of output points from conversion */
 
 	if (Ctrl->C.shift && Ctrl->F.active) {	/* Use same units in -C and -F */
-		Ctrl->C.easting *= u_scale;
+		Ctrl->C.easting  *= u_scale;
 		Ctrl->C.northing *= u_scale;
 	}
+	if (Ctrl->C.m_origin) {	/* Use same units in -C and -F */
+		m_standard_y_value = GMT->current.proj.j_yc;	/* Special Mercator adjustment for measuring distance relative to standard latitude */
+		if (Ctrl->F.active)	/* Use same units in -C and -F */
+			m_standard_y_value *= fwd_scale;
+	}
 
 	if (Ctrl->L.active)	{	/* Possibly adjust output types */
 		if (Ctrl->L.mode == GMT_MP_GIVE_FRAC)	/* Want fractional point locations */
@@ -1258,6 +1272,8 @@ EXTERN_MSC int GMT_mapproject (void *V_API, int mode, void *args) {
 				in[GMT_X] -= Ctrl->C.easting;
 				in[GMT_Y] -= Ctrl->C.northing;
 			}
+			if (Ctrl->C.m_origin)	/* Special Mercator adjustment for measuring distance relative to standard latitude */
+				in[GMT_Y] += m_standard_y_value;
 			if (Ctrl->N.active) {
 				out[GMT_X] = in[GMT_X];
 				out[GMT_Y] = gmt_lat_swap (GMT, in[GMT_Y], lat_mode);
@@ -1366,6 +1382,8 @@ EXTERN_MSC int GMT_mapproject (void *V_API, int mode, void *args) {
 					out[GMT_X] += Ctrl->C.easting;
 					out[GMT_Y] += Ctrl->C.northing;
 				}
+				else if (Ctrl->C.m_origin)	/* Special Mercator adjustment for measuring distance relative to standard latitude */
+					out[GMT_Y] -= m_standard_y_value;
 				if (GMT->current.proj.three_D) {
 					double xx = out[GMT_X], yy = out[GMT_Y];
 					gmt_xyz_to_xy (GMT, xx, yy, gmt_z_to_zz (GMT, in[GMT_Z]), &out[GMT_X], &out[GMT_Y]);
diff --git a/test/psbasemap/merc_origin.ps b/test/psbasemap/merc_origin.ps
index dd45f6dd324..379452f2b92 100644
Binary files a/test/psbasemap/merc_origin.ps and b/test/psbasemap/merc_origin.ps differ