diff --git a/doc/rst/source/grdinfo.rst b/doc/rst/source/grdinfo.rst
index 642349f9e5c..ec8ef2db727 100644
--- a/doc/rst/source/grdinfo.rst
+++ b/doc/rst/source/grdinfo.rst
@@ -19,7 +19,7 @@ Synopsis
 [ |-G| ]
 [ |-I|\ [*dx*\ [/*dy*]\|\ **b**\|\ **i**\|\ **r**] ]
 [ |-L|\ [**0**\|\ **1**\|\ **2**\|\ **p**\|\ **a**] ]
-[ |-M| ]
+[ |-M|\ [**c**\|\ **f**] ]
 [ |SYN_OPT-R| ]
 [ |-T|\ [*dv*]\ [**+a**\ [*alpha*]]\ [**+s**] ]
 [ |SYN_OPT-V| ]
@@ -65,8 +65,8 @@ Optional Arguments
     *name w e s n {b t} v0 v1 dx dy {dz} nx ny {nz}* [*x0 y0 {z0} x1 y1 {z1}*] [*med scale*] [*mean std rms*] [*n\_nan*] *registration gtype*
 
     The data in brackets are
-    output only if the corresponding options |-M|, **-L1**, **-L2**,
-    and |-M| are used, respectively, while the data in braces only apply if
+    output only if the corresponding options |-M| (with no directive), **-L1**, and **-L2**
+    are used, respectively, while the data in braces only apply if
     used with 3-D data cubes. Use **-Ct** to place file *name*
     at the end of the output record or **-Cn** to only output numerical
     columns.  The *registration* is either 0 (gridline) or 1 (pixel),
@@ -145,9 +145,12 @@ Optional Arguments
 
 .. _-M:
 
-**-M**
+**-M**\ [**c**\|\ **f**]
     Find and report the location of min/max *v*-values, and count and
-    report the number of nodes set to NaN, if any.
+    report the number of nodes set to NaN, if any [Default]. Use directive
+    **f** to instead force an update of the *v*-value min/max by reading the
+    matrix, or use **c** for conditionally doing so if the header information
+    does not contain a valid *v* range.
 
 .. |Add_-R| replace:: Using the |-R| option will select a subsection of the input grid(s). If this subsection
     exceeds the boundaries of the grid, only the common region will be extracted. For cubes you must also
diff --git a/src/grdinfo.c b/src/grdinfo.c
index 183478962f4..d9184a4049b 100644
--- a/src/grdinfo.c
+++ b/src/grdinfo.c
@@ -48,6 +48,11 @@ enum Opt_C_modes {
 	GRDINFO_NUMERICAL	= 1,
 	GRDINFO_TRAILING	= 2};
 
+enum Opt_M_modes {
+	GRDINFO_FORCE_REPORT	= 1,
+	GRDINFO_FORCE			= 2,
+	GRDINFO_CONDITIONAL		= 3};
+
 struct GRDINFO_CTRL {
 	unsigned int n_files;	/* How many grids given */
 	bool is_cube;
@@ -77,8 +82,9 @@ struct GRDINFO_CTRL {
 		unsigned int status;
 		double inc[2];
 	} I;
-	struct GRDINFO_M {	/* -M */
+	struct GRDINFO_M {	/* -M[c|f] */
 		bool active;
+		unsigned int mode;	/* 1 is force, 2 is conditional */
 	} M;
 	struct GRDINFO_L {	/* -L[0|1|2|p] */
 		bool active;
@@ -112,7 +118,7 @@ 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_Usage (API, 0, "usage: %s %s [-C[n|t]] [-D[<offx>[/<offy>]][+i]] [-E[x|y][+l|L|u|U]] [-F] [-G] [-I[<dx>[/<dy>]|b|i|r]] [-L[a|0|1|2|p]] "
-		"[-M] [%s] [-T[<dv>][+a[<alpha>]][+s]] [%s] [%s] [%s] [%s] [%s]\n", name, GMT_INGRID, GMT_Rgeo_OPT, GMT_V_OPT, GMT_f_OPT, GMT_ho_OPT, GMT_o_OPT, GMT_PAR_OPT);
+		"[-M[c|f]] [%s] [-T[<dv>][+a[<alpha>]][+s]] [%s] [%s] [%s] [%s] [%s]\n", name, GMT_INGRID, GMT_Rgeo_OPT, GMT_V_OPT, GMT_f_OPT, GMT_ho_OPT, GMT_o_OPT, GMT_PAR_OPT);
 
 	if (level == GMT_SYNOPSIS) return (GMT_MODULE_SYNOPSIS);
 
@@ -158,7 +164,9 @@ static int usage (struct GMTAPI_CTRL *API, int level) {
 	GMT_Usage (API, 3, "p: Report mode (lms) and LMS-scale (MAD w.r.t. mode) of data set.");
 	GMT_Usage (API, 3, "a: All of the above.");
 	GMT_Usage (API, -2, "Note: If grid is geographic then we report area-weighted statistics.");
-	GMT_Usage (API, 1, "\n-M Search for the global min and max locations (x0,y0{,z0}) and (x1,y1{,z1}).");
+	GMT_Usage (API, 1, "\n-M[c|f]");
+	GMT_Usage (API, -2, "\nSearch for the global data min and max locations (x0,y0{,z0}) and (x1,y1{,z1}) [Default]." 
+		" Append c to only determine data min/max range if missing from the header, or f to force that search to override the header range.");
 	GMT_Option (API, "R");
 	GMT_Usage (API, 1, "\n-T[<dv>][+a[<alpha>]][+s]");
 	GMT_Usage (API, -2, "Print global -Tvmin/vmax[/dv] (in rounded multiples of <dv>, if given). Optional modifiers:");
@@ -310,9 +318,17 @@ static int parse (struct GMT_CTRL *GMT, struct GRDINFO_CTRL *Ctrl, struct GMT_OP
 						Ctrl->L.norm |= (1+2+4); break;
 				}
 				break;
-			case 'M':	/* Global extrema */
+			case 'M':	/* Global extrema and|or update missing header data range */
 				n_errors += gmt_M_repeated_module_option (API, Ctrl->M.active);
-				n_errors += gmt_get_no_argument (GMT, opt->arg, opt->option, 0);
+				switch (opt->arg[0]) {
+					case 'c':	Ctrl->M.mode = GRDINFO_CONDITIONAL;	break;
+					case 'f':	Ctrl->M.mode = GRDINFO_FORCE;		break;
+					case '\0':	Ctrl->M.mode = GRDINFO_FORCE_REPORT;	break;
+					default:
+						GMT_Report (API, GMT_MSG_ERROR, "Option -M: Unrecognized modifier %s\n", opt->arg);
+						n_errors++;
+						break;
+				}
 				break;
 			case 'Q':	/* Expect cubes is no longer an option as we detect it automatically */
 				break;
@@ -623,7 +639,7 @@ EXTERN_MSC int GMT_grdinfo (void *V_API, int mode, void *args) {
 		n_cols = (is_cube) ? 8 : 6;	/* w e s n {b t} w0 w1 */
 		if (!Ctrl->I.active) {
 			n_cols += (is_cube) ? 6 : 4;				/* Add dx dy {dz} n_columns n_rows {n_layers} */
-			if (Ctrl->M.active) n_cols += (is_cube) ? 7 : 5;	/* Add x0 y0 {z0} x1 y1 {z1} nnan */
+			if (Ctrl->M.mode == GRDINFO_FORCE_REPORT) n_cols += (is_cube) ? 7 : 5;	/* Add x0 y0 {z0} x1 y1 {z1} nnan */
 			if (Ctrl->L.norm & 1) n_cols += 2;	/* Add median scale */
 			if (Ctrl->L.norm & 2) n_cols += 3;	/* Add mean stdev rms */
 			if (Ctrl->L.norm & 4) n_cols += 2;	/* Add mode lmsscale */
@@ -705,7 +721,7 @@ EXTERN_MSC int GMT_grdinfo (void *V_API, int mode, void *args) {
 			GMT->current.io.col_type[GMT_OUT][n] = gmt_M_type (GMT, GMT_IN, n);	/* Since grids may differ in types */
 
 		if (num_report && n_grds == 0) {	/* Need to prepare col_type for output */
-			if (Ctrl->M.active) {	/* Will write x,y[,z] min and max locations */
+			if (Ctrl->M.mode == GRDINFO_FORCE_REPORT) {	/* Will write x,y[,z] min and max locations */
 				GMT->current.io.col_type[GMT_OUT][x_col_min] = GMT->current.io.col_type[GMT_OUT][x_col_max] = GMT->current.io.col_type[GMT_OUT][GMT_X];
 				GMT->current.io.col_type[GMT_OUT][y_col_min] = GMT->current.io.col_type[GMT_OUT][y_col_max] = GMT->current.io.col_type[GMT_OUT][GMT_Y];
 				if (is_cube) GMT->current.io.col_type[GMT_OUT][z_col_min] = GMT->current.io.col_type[GMT_OUT][z_col_max] = GMT->current.io.col_type[GMT_OUT][GMT_Z];
@@ -716,7 +732,16 @@ EXTERN_MSC int GMT_grdinfo (void *V_API, int mode, void *args) {
 		}
 		n_grds++;
 
-		if (Ctrl->E.active || Ctrl->M.active || Ctrl->L.active || subset || Ctrl->D.mode || (Ctrl->T.mode & 2)) {	/* Need to read the data (all or subset) */
+		if (Ctrl->M.mode == GRDINFO_CONDITIONAL) {	/* Conditionally read and find min/max if not in header */
+			if (doubleAlmostEqualZero (header->z_min, header->z_max)) {	/* Force search */
+				GMT_Report (API, GMT_MSG_WARNING, "No actual range for data in header - must read matrix and determine range\n");
+				Ctrl->M.mode = GRDINFO_FORCE;
+			}
+			else	/* else the header has the data range; no need to read file */
+				GMT_Report (API, GMT_MSG_DEBUG, "Found valid actual data range in header - no need to read matrix\n");
+		}
+
+		if (Ctrl->E.active || Ctrl->M.mode || Ctrl->L.active || subset || Ctrl->D.mode || (Ctrl->T.mode & 2)) {	/* Need to read the data (all or subset) */
 			if (is_cube) {
 				if (GMT_Read_Data (API, GMT_IS_CUBE, GMT_IS_FILE, GMT_IS_VOLUME, GMT_DATA_ONLY, wesn, opt->arg, U) == NULL) {
 					Return (API->error);
@@ -779,7 +804,7 @@ EXTERN_MSC int GMT_grdinfo (void *V_API, int mode, void *args) {
 
 		if (Ctrl->T.mode & 2) strncpy (grdfile, opt->arg, PATH_MAX-1);
 
-		if (Ctrl->M.active || Ctrl->L.active) {	/* Must determine the location of global min and max values */
+		if (Ctrl->M.mode == GRDINFO_FORCE_REPORT || Ctrl->M.mode == GRDINFO_FORCE || Ctrl->L.active) {	/* Must determine the [location of] global min and max values */
 			uint64_t ij_min, ij_max, here = 0, node;
 			unsigned int col, row;
 			gmt_grdfloat *data = (is_cube) ? U->data : G->data;
@@ -816,6 +841,10 @@ EXTERN_MSC int GMT_grdinfo (void *V_API, int mode, void *args) {
 			}
 			else	/* Not a single valid node */
 				x_min = x_max = y_min = y_max = z_min = z_max = GMT->session.d_NaN;
+			if (Ctrl->M.mode == GRDINFO_FORCE) {	/* Update header */
+				header->z_min = v_min;
+				header->z_max = v_max;
+			}
 		}
 
 		if (Ctrl->L.norm && gmt_M_is_geographic (GMT, GMT_IN)) {	/* Must use spherical weights */
@@ -913,7 +942,7 @@ EXTERN_MSC int GMT_grdinfo (void *V_API, int mode, void *args) {
 				out[col++] = header->z_min;			out[col++] = header->z_max;
 				out[col++] = header->inc[GMT_X];	out[col++] = header->inc[GMT_Y];	if (is_cube) out[col++] = U->z_inc;
 				out[col++] = header->n_columns;		out[col++] = header->n_rows;		if (is_cube) out[col++] = header->n_bands;
-				if (Ctrl->M.active) {
+				if (Ctrl->M.mode == GRDINFO_FORCE_REPORT) {
 					out[col++] = x_min;	out[col++] = y_min;	if (is_cube) out[col++] = z_min;
 					out[col++] = x_max;	out[col++] = y_max;	if (is_cube) out[col++] = z_max;
 				}
@@ -923,7 +952,7 @@ EXTERN_MSC int GMT_grdinfo (void *V_API, int mode, void *args) {
 				if (Ctrl->L.norm & 2) {
 					out[col++] = z_mean;	out[col++] = z_stdev;	out[col++] = z_rms;
 				}
-				if (Ctrl->M.active) {
+				if (Ctrl->M.mode == GRDINFO_FORCE_REPORT) {
 					out[col++] = (double)n_nan;
 				}
 				if (Ctrl->L.norm & 4) {
@@ -975,7 +1004,7 @@ EXTERN_MSC int GMT_grdinfo (void *V_API, int mode, void *args) {
 					gmt_ascii_format_col (GMT, text, (double)header->n_bands, GMT_OUT, GMT_W);
 					strcat (record, text);	strcat (record, sep);
 				}
-				if (Ctrl->M.active) {
+				if (Ctrl->M.mode == GRDINFO_FORCE_REPORT) {
 					strcat (record, sep);	gmt_ascii_format_col (GMT, text, x_min, GMT_OUT, GMT_X);	strcat (record, text);
 					strcat (record, sep);	gmt_ascii_format_col (GMT, text, y_min, GMT_OUT, GMT_Y);	strcat (record, text);
 					if (is_cube) { strcat (record, sep);	gmt_ascii_format_col (GMT, text, z_min, GMT_OUT, GMT_Z);	strcat (record, text); }
@@ -992,7 +1021,7 @@ EXTERN_MSC int GMT_grdinfo (void *V_API, int mode, void *args) {
 					strcat (record, sep);	gmt_ascii_format_col (GMT, text, z_stdev, GMT_OUT, GMT_Z);	strcat (record, text);
 					strcat (record, sep);	gmt_ascii_format_col (GMT, text,   z_rms, GMT_OUT, GMT_Z);	strcat (record, text);
 				}
-				if (Ctrl->M.active) { sprintf (text, "%s%" PRIu64, sep, n_nan);	strcat (record, text); }
+				if (Ctrl->M.mode == GRDINFO_FORCE_REPORT) { sprintf (text, "%s%" PRIu64, sep, n_nan);	strcat (record, text); }
 				if (Ctrl->L.norm & 4) {
 					strcat (record, sep);	gmt_ascii_format_col (GMT, text, z_mode,   GMT_OUT, GMT_Z);	strcat (record, text);
 					strcat (record, sep);	gmt_ascii_format_col (GMT, text, z_lmsscl, GMT_OUT, GMT_Z);	strcat (record, text);
@@ -1117,7 +1146,7 @@ EXTERN_MSC int GMT_grdinfo (void *V_API, int mode, void *args) {
 				}
 			}
 
-			if (Ctrl->M.active) {
+			if (Ctrl->M.mode == GRDINFO_FORCE_REPORT) {
 				if (v_min == DBL_MAX)  v_min = GMT->session.d_NaN;
 				if (v_max == -DBL_MAX) v_max = GMT->session.d_NaN;
 				sprintf (record, "%s: v_min: ", HH->name);
@@ -1159,7 +1188,7 @@ EXTERN_MSC int GMT_grdinfo (void *V_API, int mode, void *args) {
 				         (header->z_max - header->z_add_offset) / header->z_scale_factor);
 			}
 			GMT_Put_Record (API, GMT_WRITE_DATA, Out);
-			if (n_nan || Ctrl->M.active) {
+			if (n_nan || Ctrl->M.mode == GRDINFO_FORCE_REPORT) {
 				double percent = 100.0 * n_nan / header->nm;
 				sprintf (record, "%s: %" PRIu64 " nodes (%.1f%%) set to NaN", HH->name, n_nan, percent);
 				GMT_Put_Record (API, GMT_WRITE_DATA, Out);